The whole Descent series is pretty sublime. Except for Descent 1, which made me violently nauseous to play (mostly due to the lack of the guidebot, and I wasn't used to playing games like that). I still played the hell out of it, though - I remember playing it on line with a friend of mine and my mother and father would come in and exclaim, "You're playing with JOSH(my friend's name)?". Repeat that a couple times per session and you'll capture their general bemusement of the whole concept of "online" being synonymous with MAGIC. The Freespace spin-off has yet to be topped IMHO too. There's nothing quite like being stuck between to capital ships blasting each other to bits. I played Descent 3 quite a bit as well - I loved co-op.
As far as bastard games...I wished you were talking about bastard games that you have no idea why they are in your collection. Since I want to bitch about it, I'm going to sneak it in here and then answer your question
. Mahou Tsukai ni Naru Houhou for the Saturn. What the hell. I bought it because I thought it was 2D, and it was a local store. I still haven't played it. I don窶冲 think I ever will. It look horrendous.
I'd have to say Quake (PC) though. I am still enamored with the blood sprays, and the speed. Quake is my idea of a "pure" FPS - no gimmicks, no story (those three paragraphs of nonsense in the readme don't count), no fancy weapons, just pure carnage. Plus people keep making ridiculous enhancements for it, so there窶冱 always an excuse to bust it out.