The primary issue with AP Ezreal is his lack of reliable waveclear. Against somebody like lux, morgana, malzahar, you are basically pushed to your turret the entire laning phase, scrambling to last hit minions. It's difficult to actually harass your lane opponent at all because of this, and you can end up losing lane pretty easily. It limits your roam potential, and limits your gold income overall. Auto-attacks don't do much, W doesn't hit minions.. E costs so much mana, and his ultimate can't even clear an entire minion wave. The most extreme opponent IMO would be Twisted Fate. His one ability can nearly wipe out an entire line of minions. It's pretty difficult to lane against that.
His W width nerf is pretty noticeable, as well. It would be nice if that was reverted. If he misses that, he doesn't do much damage at all. It also feels like his W doesn't start doing damage until a few points into it.. feels like a waste of mana until then... but if you harass too much with it you'll OOM quickly.
I feel like Sheen getting cheaper on the PBE will help AP Ezreal out a little, though, since Lich Bane is so good on him. But, overall, I used to really love AP Ezreal... but his laning phase is just so awful, and he has few favorable matchups. He can't really be played in any other lane, either.
The best idea that I've heard (but it ends up being a "cheap fix") would be to have his W apply a debuff to minions that it hits, that Ezreal can auto-attack for more damage. Basically, the same thing Lux has. The only down-side is that to apply this debuff, it would have to "hit minions" which would feel strange if it then didn't stack his passive... but stacking his passive on minions would be too powerful, unless he can only generate one stack per ability, from minions.