The series is now on its 3rd game, unreal tournament 2004 (last was ut2003, and before that the original UT) and soon to release UT2005 (Think sports games). UT2004 features fast-paced, solo and team oriented gameplay, as well as good implementation of vehicles.
The game has almost no single player gameline, and focuses on battlefield style gameplay with implementaion of bots. There are many different gamemodes; including deathmatch, team deathmatch, bombing run, capture the flag, last man standing, mutant, double domination, onslaught and assualt.
Onslaught and assualt both feature vehicluar warfare, and introduce single crew and multi crew vehicles; including the scorpion, manta, raptor, goliath, hellbender, and levithian.
Unreal tournament is designed with a much faster, explosive gameplay than titles like counterstrike and battlefield 1942. Most maps are medium sized and will leave you to encounter enemies every 2-10 seconds or so, and with constant respawning, (not round based) this means that it takes fast reflexes and sharp wit.
The gameplay also features various acrobatic stunts, such as the ability to dodge (double tap a dirction key), wall jump (dodge after jumping near a wall, thereby pushing your characetr off the wall in a flip or cartwheel) and dodge jumping (dodge, then jump to send your character launching through the air at a significant rate)
There are also various power ups, such as double damage, shields, health pickups, health viles, kegs of health and adrenaline. The adrenaline powerups increase you adrenaline level to a max of 100, at which point you can activate one of four combos (speed, beserk, invisible, and booster)
The above are based on UT2004, which obviously offers more features than UT2003 and UT Classic, however these prequels can be understood by thier loyal sequal, ut2004.
Overall, UT contains enoguh features to create dynamic, diverse, and broad gameplay, complete with tons of maps (UT2004 comes with well over 100).