Let's look at the negatives first. The cost is insane! Well, for a deck that isn't focused around core energy. 4 Cores is a very steep price, fortunately, that is the only negative.
Now to the positives. Let's read it "Deal 2 damage to all enemy characters." That's amazing! Most skills only damage active characters but this lets you smack ALL enemy characters! That's active and reserved characters! This attack can' be dodged and guaranteed damage regardless of DEF. So that pesky monster with insane DEF, those players that like to dodge everything, staring against an army of monsters and you don't have the numbers to keep up? All that doesn't matter with this skill, they all take damage!
Use this skill 5 times and it's basically game over for your poor opponent. Also it's negative is also a hidden positive. The high cost means you can attempt a manual charge with a much higher success rate so you can launch another Petal Frenzy sooner!