We played this game a great deal when it was first launched. It has some very satisfying dynamics, ranging from the responsiveness of the avatar, through the ability to easily mod the game elements with mutators (such as gravity and weapons) to being able to unleash total mayhem by hacking the amount of bots onscreen (if you don't have 60+ friends free for an evening).
If you have this game and also have a high end rig, bring down the console with the tilde key (~) and enter "addbots x", where x is the numeric amount of bots that you want. I added 64 the other day on my monster rig and the game was flawless, fast and a complete fragfest.
They don't seem to be able to make games like this today. It's a sign of the times and many games have a lot of polish, but little "feel". UTGOTY has all the elements of a great fragging game with countless mods and mutators out there. If you want to add Mutators in Vista, make sure you grab the "UMOD TOOL.". I have version 1.9 and it works well in Vista 64Bit.