The most versatile, elegant, and powerful offering currently on the market. Mac OS X possesses a solid UNIX core for server work and tweaking, and yet also has a beautifully thought out and designed interface called Aqua. The current version as of this posting is 10.3, and 10.4 will be coming out soon. 10.4 will feature metadata searching and Coreimage GPU-based real-time image processing
Worst Unreal Tournament ever. Completely butchered the feel of the game, upset the weapon balance, and included a paltry number of maps and a bunch of useless gametypes. Unreal Tournament 2004 fixed all the wrongs done in UT2k3, but unfortunately wasn't able to woo back all the players alienated by UT2k3.
Basically, UT2k3 showed off Unreal Engine 2's new graphics, while UT2k4 used those graphics to illustrate a game worthy of the Unreal Tournament series.