Thanks for all the replies and feedback and sorry for replying so late - I'm currently travelling through south east asia and don't have internet most times. That's the reason I haven't been working on my own startup as well. Last fall for me it was "maybe get chosen by yc and start working on the thing than or do a 6 month sabbatical first (after 3 years working for the man) and than start on my own.
So right now I think it will probably be 2starting on my own but working on something else2 :(
I completely agree with everybody that stated that the team is usually more important than the idea and that execution trumps everything.
Still the timing of the whole affair feels really bad to me. Having had this idea in mind for quite sometime (besides lots of others), finally quitting the job, submitting it to yc and now see it implemented by someone else from just that cycle where I was turned down I must say I kinda feel fucked - to be that blunt.

Everybody saying that I can still do it (or similar) is right in principle, but to me the most important part of yc has always not been about the funding money but the mentoring and networking and actually beeing in the valley. Coming from germany of course I can start here as well, but pg himself is the first to tell you about how much of a difference this is.
So looking to go against an now established player with all those advantages on his side doesn't seem like that good of an option and the best my startup could achieve would probably be to be taken as "the lame german rip off" (there are a lot of them actually) by the public.

So in the end - not trying to read to much into it: the best conclusion I can come up with now is that apparently yc thinks that I and my team suck so much that, even when we come up with an idea like that, that is worth funding when someone else does it, we still stand no chance.
So sadly I must say that I will probably not apply next time as I don't see how I could much improve on that situation.

BTW: Here is a part of my yc application so you can better understand where I'm coming from and judge for yourself.

What is your company going to make?
Create a plattform to supply existing online networks with casual flash games which integrate into their social tree. Core business will not be in game development but in providing the service in form of customizable widgets to the social network site owners and users and ...
Think "distributed kongregate"

For big plattforms like facebook and myspace that allow their users to integrate widgets of there own this means simply to create game widgets according to their api (i.e. facebook apps) and allow users to add those to their profiles.
But unlike other simple games on facebook/myspace we want to make these games aware of the underlying social plattform by doing things like showing only the scores of the users friends in the high score table.

For smaller plattforms which don't allow user widgets (think NINQ and small self-developed local portals) we will market to the plattform owners to integrate a free full grown casual game portal in their site in form of a big widget which will occupy a whole page that they can then call THEIR game section. This big arcade widget will display games in different categories, most played games and most succesfull players - FOR THAT SOCIAL SITE ALONE.

...