Metaball (click for info and screens):
Interesting mix of games like Sonic The Hedgehog and Marble Madness with its own unique feel and gameplay. One of the few creations I’d place right up there with titles such as Nights Into Dreams for its excellent concept and execution. A MUST download for every Unreal Tournament 2004 owner (Yes, it’s an UT2004 mod). For more information about the actual gameplay click here.
Ofcourse, playing it is nothin like reading about it
For a list of recent (only recent, not older) UT2004 mod releases click here (edit: That post is not updated anymore so if you want to remain current about news and releases, keep checking the website in my sig).
From the Mods on that page I’d especially recomment Metaball, Damnation, Alien Swarm, Red Orchestra, Frag.Ops, Air Buccaneers, Deathball, Troopers, Eden Eclipse, Piddly’s Chance, Clone Bandits.
Naturally, I haven’t tried all of them so just visit every working website and try out what you find interesting for yourself. It’s free anyway
I love modable games