The only problem I have with Evelynn is her stealth mechanic. I don't like the fact that champions can see her from so far away. Other than that, I've racked up plenty of kills with her.
The problem is that Evelynn is
her stealth mechanic. Without that she's a mediocre tanky dps option with a bunch of steroids, meaning any
other tanky dps champion is a better option because her new stealth is shit.
She's got pretty good damage output (after being significantly fed/farmed; her early game is absolute crap), but almost nothing in the way of CC to protect herself or halt a runner, no gap-closer and negligible burst potential. Once she actually latches onto someone she can rip into them pretty hard and her movespeed bonuses are hilarious (I was able to chase a Highlander-buffed Yi through his allied Heimerdinger's frost turrets and was still running FASTER than Yi), but she's altogether lackluster without the ability to actually sneak up on someone to get those first speed-boosting hits in.
They need to make the radius of detection on her stealth smaller or add a delay to how long you can be near a champion before they detect you or SOMETHING. The current version of her stealth is almost useless; it's basically just a bush you carry around with you. Sure, it can enable some ganks the enemy team might have otherwise seen coming, but you're in the fog of war for 95% of that time anyway, so being invisible is redundant up until the point where you actually BENEFIT from it, which is when they can see you. -.-
The Eve rework is a mess.