I do stuff on UT2004. Most are weapons or vehicles. Also did some characters. Never thought about publishing it as it depended on lots of custom content. I am currently waiting for feedback to make standalone versions and release them here.
Have you ever noticed how splitscreen kills all the tactical part of MW3 multiplayer?
Think about the ambushes you've tried to make but failed simply because your foe knew about it (not necessarily splitscreen here).
The game is then reduced to only a chaotic shootout, all the while knowing everyone's location, be it by the "Radar Always On" option or just by looking at the other screens.
Try to place a Bouncing Betty, Claymore, C4 or any placeable killstreak and see it be destroyed by the enemy (doesn't matter how well it is hidden) to see what I am speaking of.