I have played it for 100 hours, so i can pretty much give some real thought on it.
Before anything, you must note: Don't listen to the majority (Peoples are dumb, often), but to what seems the best review(er)s for you. Video games is an art, and art is about personal taste.
Also, keep in mind i played the PC versions, no Xbox360 nor PS3. Also 2, the game is badly optimized for ATI, and i have an ATI. Though it work fine, not great, just fine. I've got to keep V-sync off, and Textures and shadow at Medium to keep a decent FPS (Frame Per Seconds, for the noobies) For some ATI peoples it work really bad, and some say it's perfect. Though now with the few patch they did, it seems to work ok for ATI users (Once again not great, but ATI and SD are working on it, as it is said)
Now what i think about Brink (Lot of details about every thing in the game, if you want a short version, read the last paragraph):
The design and art style is great, and "fresh" as some said. Everything is exaggerated, the faces, and bodies... Even the weapons are. The "Euston" looks like an M4, but... with exaggerated features. The game is far from realism, and it actually work perfectly. The weapons are really "uber". When you shoot with a gun, you know you are not shooting beans and rice balls. It's loud, flashy, shaking, and plainly awesome. Firing a shotgun in Brink is like firing a flak canon in a closed room.
The Resistance Weapon theme is my favorite, personally.
The cinematic and the pre and post game cinematic are short, but good and you know what you are fighting for with them (Don't lie to me, we rarely knew why we where shooting at other peoples, and exploding "objectives" in most FPS) and they are giving hints to the story of the Arks. In Single player you will see the same guys doing the speech (And you in the background) but in multiplayers, the cinematic will use characters from other players (And you in the background once again). Good touch. The voice acting is really good too (In the English version at least. I know that in French it sounds somewhat horrible for what i have heard of it, but nothing surprising from French voices actors) and this Resistance guy in the Reactor cinematic really give you some will to rush-in: "We will have justice... In this world... or the next!" (Dude, now that's a way to speak to real mens. No time for diplomacy now.)
The Character customization is not as powerful as how APB's customization was, but it's good enough, and actually, maybe better suited for the art style of the game. You can have really different peoples in-game. And both side (Resistance and Security) are really different. You know who you are shooting at. Of course Security's cloth looks more like Police and armies uniform, while Resistance looks like post-apocalyptic fashion (Having crap cloths doesn't mean you can't looks cool in it) Once again, the design works really well. Your body type change how you can use the SMART movements, but i'll talk about it later on.
The maps are well done, some are unbalanced giving an advantage to a side (Either the whole map, or in some part of it) but they are all doable. And personally, i don't have much problem about it. There is a good number of different main / secondary objectives, though more could be better. You can hack computers, open or hack safe, escort a "VIP" NPC, Take one object from point A to point B, Repair things, Blow up things. And a great numbers of side objectives (which are mostly to hint you at what you can do as your current class, and how to help your team) Buff damage to players, hack enemies communications, Revive players, etc... And you will often find new things, or how to improve yourself even if you played a map for a long time. (New way to get from point A to B, where to plant Mines / satchels, etc) Also, the maps have lots of little details, like in Left 4 dead. You will find Newspaper, and tags on walls (In different languages) which will give you some more information about the Ark. The maps also looks like what they are supposed to be at first look, no mistake possible: A shanty town, an Airport, a Security building, a Shipyard, etc... Most of others FPS fail at this, since they are not taking much care about their art style.
The Weapons and Skills are diversified enough, so you have plenty to try, and use. As for the weapons: There is Pistols, SMG, Shotguns, Assault rifle, Light rifle (Snipers) Machine guns, and Grenade launchers. Most of them have equipment that can be unlocked then used on it (Silencers, Sights, Red dots, Underslung grenade launchers, etc) For the skills: You have Overall skills (All class can use them) and class based skills (Soldiers, Engineers, Medics, and Operative) that can only be used when you have the said Class selected (You can change class before and while playing) All the skills are useful, and all the weapons too, except they are more situational (Like the grenade launchers, which are better for mob controlling) they are well balanced, except one or two (Like the Carb9, which is talked over and over in forums) but nothing really nerve cracking. And actually, it's the first game where grenade launcher are well balanced.
The Leveling, or whatever you want to call it, is not a big part of the game, or at least not what will keep you playing (Nothing like RPGs) For now it's 20 levels, which you can gain fairly easily and you can max one character quickly (A few days of playing for the casual players) so it's more like a way to help you get used to your gear.
The Factions have no gameplay differences, they have basically the same weapons and skills. They look different, but are not. You may like it or not, but it's actually (Infinitely) easier for the game developers to have both side balanced in terms of weapons and skills, since they are basically the same. The weapons have different looks... and sounds, depending on what faction you are on. It's another little but nice touch. Factions have different stories, of course. And it's interesting to see both sides. And when playing you will win Audio logs, which can be listened whenever you want, and is about peoples talking about their lives before and while being on the Ark. Peoples who like to have some story in their game will like it (I do) others will just ignore it. Listening those audio logs may change your views on each sides, or confirm what you were thinking.
The Singleplayer is just the multiplayer with bots. It's a good training, but a real singleplayer would have been way better, even more with a Story as interesting as the one of the Ark. Though, i think we can't really blame Splash damage for this point: Brink is a new IP, and Splash damage is no where near the biggest companies, and probably can't spend their time doing everything. They have chosen a multiplayers game, to have a bigger replaying value, and which they already had some experience in. I think it's better that way. Still, the lack of real singleplayer is a bad point (With an excuse).
The multiplayer is where the game shine. You have fun, maps and objectives are diversified, there is lot of actions, some stressing moment (Mostly as an Operative) and some "Dammit, nice one." moment for your enemy (Yes, you will find some actions of your enemies worth your death, and say it to him)
The community looks good for me, but once again i can't stay for others platforms... But at least for PCs, in Europe, i rarely find *ssh*les and idiots in-game. Surprising enough, peoples can even be friendly and help newbies. What the hell? Did i fell in another dimension where the internet is nice to others? Joking aside, it may be because the Brink players population is small. I'm not going to lie, but this game is really far from the mainstream, and have not a big fanbase, but at least it looks nice. Like the player base of Killing floor (Small, but nice) Though, have no fear, there is way enough peoples to play with.
One sensible subject, the DLCs... Well... They are free. Not so sensible anymore? For now, the first one is free, and will add two new "Archetypes" (Characters customization), Two new weapons modifications, Two new maps, and will Raise the level cap (From 20 to 24 i think?). Probably with an updates to fix some things. The next ones... I don't know, i hope they will make free DLCs of course, but showing support to a dev-team which bring some original stuff in an era of Mainstream games can be good too (But paying more than others doesn't have to come with more powers. Pay to win = Not a good thing)
Last, but not least, the SMART system. This was probably what you where the most looking for, since it's the biggest change the game is supposed to make for the FPS genre. And actually... it should does. It should? Not simply "It does" or "It does not"? Yes it should. Why? Because big game companies often goes for the mainstream, not the new original stuff. And since Brink isn't Mainstream, they will probably ignore it. But actually... Now..; I only think with SMART. I can't f*cking play another FPS without thinking "Dammit, if i had the SMART..." SMART mean Smooth Movement Across Random Terrain, and it actually say it all. You really move smoothly across random terrain. You can move to some spot, or area which seems unreachable for common FPS movement. But in Brink, after a while, you will think with SMART, and literally see what you have to do to get "here" and "there". And the SMART system work perfectly for the FPS genre. It's nothing like in the Assassin's creed series, and it's not quite like Mirror's edge (Both great games) you don't have to think much about what you are doing. It's natural. You can improve your SMART skill by using a few more tricks to get somewhere (Jumping before climbing the wall help you to go up faster, as an example) but even as a total noobie, you will be able to follow your teammates.
Note that you are not going to do some epic move. It's Parkour, you climb, slide, and wall jump, you don't fly over the sky, and goes all Spiderman.
Also, you body type change what you can do with the SMART system. Being a light body type you can do everything, Climb the tallest wall, and wall jump; You are also faster (But you have less health) The medium type can climb wall that stop around his head, or a bit above. No wall jump. The Heavy body type can only mantle "walls" around is waist. He can slide like others body type, but not as far since he is overall slower. Of course, no Wall jump either.
One bad note though, sometime you can't climb somewhere because there is an invisible wall, even though you clearly know you can go "here". It doesn't happen much, and not in important area or anything like that. So it's not a big bad point.
Overall thoughts: Brink is a great game, peoples often talk about his "Potential"... No "Potential" for me. The game use everything he have to offer (Design choices, SMART, and Teamplay) and make the game fun in many way (For your eyes, for your ears, for your enjoyment) The weapons looks and sound great, the maps are well designed but have some balance issue, the SMART works really well, the Customization is good enough (And they will add more) The music and atmosphere is awesome. The Voices acting is really good. The gameplay is solid. The teamplay come naturally. Totally Noobie friendly (You won't be afraid to play online). The Story is good, but not that much is shown. Some nice little touch. Only the graphics have some problems, actually it's the main problem of the game. ATI users can have some problems, and as i heard, Xbox360 users too. Though, they are fixing this. It's not part of the game, so you can't really judge a game only for this. The game was probably released a bit too early, and they probably were overconfident, since they did released it earlier than expected (Can be for economic issue, or pushed to do it by their publisher, though.) more testing to optimize it for most actual computers would have been good. That's the only real bad point.
Good game, worth the money, and the time spent on, but make your own idea of the game: Watch some gameplay on YouTube, read more reviews (From peoples that played the game for more than 10 seconds), go play it at a friend house, and/or rent it. Because the game is really for a particular type of gamers. Which may not be you.
-Note: Any grammatical, and whatnot, error, or anything i missed or forgot to talk about (Hell yes it's possible, even with such a wall of text)? Any personal feeling, or comment? Please voice it (Well... type it, actually)