Yay! Doom. I haven't played this game properly in about 15 years but I loved it back in the day and it must rank as one of my most played games ever.
I thought I was over Doom really, a nice bit of nostagia but generally old hat - it seems not! I came accross Skulltag and gave it a spin and the addition of modern mouselook/WASD controls with an updated graphics engine are really like a breath of fresh air. It's still as playable as ever and there's something about Doom that hits a spot other FPSs just don't; it's probably the most cathartic game ever.
So yeah, if you have a Doom WAD lying around its definitely worth a shot if you haven't already. I'm sure there're plenty of more savvy GRcaders who know about all this stuff anyway, but I just thought I'd share especially as old PC games don't get the attention they deserve. It's one of the most re-visitable retro games in my opinion and this makes it easy, even for online MP.