All the powers (adrenaline and melee powers in air) are easy to use, yes.
Your adrenaline powers are all in a sub menu, that you get to by hitting X, hit X a second time to go to the second menu. Then you hit L trigger, R trigger, or A to activate the power you want. Once you learn the characters and their adrenaline powers, then it's more of a combo to do them. For example, when I want to use Vampire with Lauren, I hit X, X, L trigger real quick and it goes off.
The melee attacks in the air are easy as well. Hit the R trigger to go flying accross the board (hold it to go farther but you are vunerable during the charge up), or hit B to do a dashing melee attack. The B button attack in the air uses 2 little bars of adrenaline, though, so if you have no adrenaline at the time, you won't be able to do it; the R trigger charge uses no adrenaline to use.