I got the Res. of evil ex.pack. If you can miss the couple of bucks it costs, then i would definitly get it. It is in the same line of Doom3 you arive at Mars and start finding your way to the end goal (what ever it is, i cant get passed one of these Hell demons at the moment). There is a new weapon a gravity gun, which works a bit like the HL2 gun.....plus that you can catch fireballs with it and torped them back to the demon (this however requires some skill and speed). Sounds are awesome, graphics too.
Doom3 could be a bit more variated (you can get borred) but somehow i can't play the game for long anyway (it is too traumatic!! Yes I'm a whimp
)
Ciao