/jerk
PQ was never released
/unjerk
In all seriousness, my biggest complaint about MB (and MBG, in particular) is that the game is just dated. The graphics are awfully outdated to the point where it just looks horrible in some cases (no proper AA, mipmapping looks terrible, low-resolution textures), and a lot of features which are taken for granted in games nowadays, such as proper controller support, are missing. Furthermore, the game runs horribly on Linux unless you can get it working in WINE, and the game also has issues in general on a lot of systems (sound glitches, etc.). The frame rate used to be locked at around 63 FPS until I recently came up with a patch that reworks the timing system. Not to mention that I also hate TorqueScript, but you can ask Jeff about that.
It would be amazing to see the game be rewritten in a modern engine, but unfortunately doing that would probably require access to the source code for the game's physics engine. People have grown so used to the quirky physics in MB that nothing else just feels quite right.
Of course, I can rant on and on, but what matters is that regardless of all that, the game is still fun to play. I think the fact that we're still talking about a game that came out in 2002 says something pretty significant.
"You know you've spelled something wrong when the only search results are Jeff convos" - HiGuy