Best until UT 2004 for its AI, Game play, Graphics, Sound, Online play and for its Replay value.
The gamespot score tells all about it. This game has a huge variety of mods and there are still few mods upon which people are still working.
Varieties of gameplay: Single player ladder + Deathmatch, CTF, Assault, Domination, Last man standing
AI: I only play with bots as i have no broadband yet. They are programmed very nicely. And they offer a great challenge at all difficulty levels. We can command them to attack, defend, or cover you or to freelance.
Graphics: Directx 7.1 makes even the slowest system play it at a high frame rate.