Though technically the successor to the 2003 edition of Unreal Tournament, UT2004 can be seen as the spiritual successor of the original Unreal Tournament and the sequel that UT2003 shouldve been.
When released, hopes were low, thanks to the almost mediocre UT2003. However, UT2004 proved itself to be a worthy successor of the UT legacy and soon established itself as the new king of the deathmatch hill.
Gametypes: Featuring the game types in UT2003, UT2004 adds a couple more to the basket. Assault makes a comeback (to thundering applause) along with a new gametype - Onslaught. Onslaught features huge terrains in which the objective is to reach and destroy the opponents base by capturing connected link nodes much in a connect-the-dots fashion. The major feature in Onslaught is the lavish use of vehicles, which are very much necessary for traversing the sprawling landscapes.
Gameplay: Improving on the already stunning gameplay of UT, UT2004 features even more mobility than the original and encourages mobility over accuracy. Double jumps and wall jumps add a bounciness which make it harder for an opponent to hit you. This is a double-edged sword and sometimes retracts from the gameplay as much as it adds to it.
Weapons: Improving on an already well-done arsenal, the weapons in UT2004 are sensible improvements over the original ones. The flak cannon is toned down, as is the rocket launcher. By the way, the original sniper rifle makes a comeback (it was missing in UT2003, replaced by the lightning gun).
Maps: Maps have been an area where the Unreal series have always dominated over anything ID throws out. Maps are much larger and provide as much entertainment as the original did. This time they went crazy and added even more varied maps like boarding alien motherships (Assault), capturing a nuclear warhead from a convoy (Assault), futuristic wastelands, junkyards and many others. Also, many of the fan favourites like Facing Towers, Deck-16, Ironic, etc make a return as remakes of the original.
Vehicles: Vehicles form an integral part of Onslaught and dont feature much in the other gametypes. However, one major exception is an Assault map which features the attacking team arriving in fighter jets to attack the alien mothership, with the defending team protecting it in alien space-fighters. This map provides for excellent dog-fights and demonstrates the versatility of the Unreal engine. Other vehicles are pretty decent and are well balanced. Trust Epic to do their games well.
Extensibility: UT2004 is as easy to mod as the original. Tons of community made mods are available and will keep the user engaged till the next iteration comes to take over the throne.
Verdict:With UT2004, Epic provides a worthy successor to the Unreal Tournament series and correct all the mistakes they did with UT2003. With no competing products from ID, UT2004 safely claims the deathmatching throne.