Someone else still plays Carmageddon? Wow. I always though that its racing and damage physics were way ahead of its time. Also, did you ever try one of those graphic mods for Quake like Tenebrae or fuhrerQuake?

I've replayed Grand Theft Auto 3 several times over (never quite getting the 100%), and Vice City about three times over (never have finished San Andreas). I've played Diablo through a couple of times (Playstation version), as well as Final Fantasy Tactics. :)

hell yes

I used to replay RPGs (Baldur's Gate 2 and Deus Ex come to mind), but I find that they're definitely not as fun the second time around and I start getting bored. I'm also getting to the point in my life where my gaming time is decreasing more and more (that's aging for you), so I have to pick and choose what I play.
I still enjoy replaying FPS games though. I've replayed Jedi Knight 2 and Half Life 2 the most, but I've replayed No One Lives Forever, Half Life 1, and a few others more than once also. JK2 and HL2 never get old for me - I've replayed each at least 3 times (JK2 probably 5 or 10).
I really love the core gameplay of the Hitman series (where's the next one?), so I never tire of replaying them as well. I like the gameplay improvements of Blood Money, but I love many of the levels from Silent Assassin and Contracts, so I replay them just as much.