Don't know about you guys, but the sound is completely broken for me in pre 5 (I mean, there's no sound at all, and the slider is at 100% as usual).
Water has changed too: every "water block" coming vertically from a source is also a source... which basically means a waterfall is an infinite water source (maybe a bug?).
I still couldn't try and fight an Enderdragon, as I can't find SinglePlayerCommands for pre 5, and I don't know what other mods may enable me to spawn one.
However, they seem to be ridiculously tough (100 hearts of life), and drop a bunch of exp orbs (and one obsidian block too, which is probably temporary).