Okay, I've uploaded a new version of the game. Currently at 3.81kB.
I've tweaked the physics a bit to make it match the original a little more closely. Note that it's still not a perfect replication of the latter's physics - the original even more sensitive than this version (though you get to play in full screen, which helps a bit). I decreased left-right sensitivity a small bit, but increased upwards and downwards forces (less air resistance, more upwards boost per flap, lower maximum upwards speed). I worry this might make it harder - I'm a bit torn between staying true to the original (which is seriously difficult) and wanting to make it accessible. Let me know what you think of the physics again, please

I've also added a couple more levels, including a final level where I allowed myself some artistic license - if you reach it, you may note it's slightly different from the others in terms of layout.

The feedback's much appreciated, everyone - keep it coming, please!
EDIT: I'd love some feedback on level order and design as well. What do you think of the order of the levels? The introduction pace for new gameplay elements? Are there any levels you don't like that I should remove in favor of new levels?
EDIT2: One more question - how's performance for everyone? Anybody seeing the game running slowly, or having drawing/buffering issues?