Gameplay is MUCH more important than graphics. Period.
I'm a big fan of the old-er school games, anyways (Worms World Party... Diablo II, etc..)
I mean, Half-life has terrible graphics, compared to some new-er titles, but I'd still much rather play HL or UT than Splinter Cell, or Halo.
(Personally, I couldn't stand halo, and never quite figured out what was so 'revolutionary' about it). In my book, Unreal Tournament and Counter-Strike are still THE BEST online FPS you can get. Or maybe that's just me, remembering those awesome LAN-parties we had every week...
Edit: dangit.. now I'm searching for my UT CD. Thanks alot. *sarcasm*