Things just got interesting: Epic Games has announced that their incredibly popular Unreal Engine 3 now works in Adobe Flash, demoing a version of Unreal Tournament 3 running inside the new Adobe Flash Player 11.
That means porting existing games to work in a browser-based solution — and there are a ton of games on Unreal Engine 3 — would be more or less turnkey.
A quick look at the screenshots provided by Epic indicate that the engine isn't as powerful as a non-browser-based engine — no big surprise there — but that it's still very much a "real" 3D experience. (I haven't yet seen the engine in motion.)
Even better, developers will be able to migrate their games from, say, iOS over to a browser-based environment without much hassle, making it possible to easily sell browser-based games that play the same games as apps on mobile devices.