Timesplitters is great because it had so many gamemodes, level creation, multiple era's of technology and a classic fps feel. Things you won't get in any modern day fps.
well, to be fair, both halo and CoD have a load of gamemodes, but they're all mostly the same.
that's one reason I like UT2004. it has a good bit of unique gamemodes, plenty of maps, and it supports the modding community.
it doesn't had more than one era of technology, but it does have a couple of groups of vehicles. well, if you download CPB2. but you should do that if you get UT2004 anyway.
dunno what a classic fps feel is. but I do prefer games like this to CoD, or halo, or anything else. UT3 is also very similar to UT2004