There's a big post on GD going in depth on this stuff as well: http://na.leagueoflegends.com/board/....php?t=2340178
Your only option for current stealth is to keep her as weak as she is right now, which I think we know the results of that. In order to make it so Evelynn can be good, we had to add a new type of stealth. No, you will not be able to walk up to someone invisibly and stun them - there's no version of that playstyle that will exist in LoL, and no matter how fun it is to do, it's dead and buried. I like to compare that to one-shotting people - it's fun to do, but doesn't enable good gameplay.
There's a lot of new exciting gameplay for the new stealth, but it's harder and more nuanced than "lolI'mminvisible". On a good note, you're stronger and not completely countered with one item :P