In response to what's been raised:
Audio: this is being worked on. The Web Audio API (already supported in Chrome & iOS 6) is as powerful as XAudio2, and we should be able to port most of the missing audio features to C2 in the near future. I've got an overhaul of the Audio object planned in order to add these features, I'm basically waiting for Firefox to implement the Web Audio API (to prove it's not a webkit-only feature that doesn't gain favour with other browser makers).
Canvas: this third party plugin might help
Per pixel collision: surprisingly few people have said they miss this in C2. Do games really absolutely have to have per-pixel collisions? I thought collision polys were acceptable in almost all cases. Can someone show me some gameplay mechanic that requires per-pixel collisions? Polys have some additional advantages such as not needing so much CPU, being able to be shared with Physics, and if we implemented shadows & lighting then it can be shared for that too (which has to be polygon based).
Sprite distortion: will probably eventually get implemented for the WebGL renderer
Color filters: can be done with WebGL, but is not easily supported in canvas2D, which is why it was moved to a shader. WebGL is in its early days; it should be much more widespread in future, and you should be able to count on it being present on some platforms eventually (e.g. maybe Android or desktop). Or you can implement canvas2D fallbacks, or just require WebGL support (check on the start screen or something). Not quite as smooth as Classic, but it does work cross-platform.
Slower performance: most games (that don't use Physics) are bottlenecked by the renderer. If you can send me a C2 project that is bottlenecked in logic, I can run some profiles and see if I can optimise it. I haven't seen many logic-bottlenecked projects in C2 though.