Ok so first, I'll just say, this is cool. I'm pretty excited about asm.js in general.

I'm sort of skeptical when they say they ported "Unreal" though. What I see there is an Unreal map viewer. I don't see any physics or AI or sound going on. The thing is about doing a map viewer, pretty much all the work is going to the graphics card, so it really doesn't matter what language you use. I think I'll be more excited when I see a demo that actually plays like a full game.