Doom 3 BFG Edition. Got it for the heck of it since it is only 5 bucks on Steam right now, I actually own the original version still, but I feel the game has aged kinda shakily, even with it being an upgraded version. It does run super smooth, some good basic features being put it such as the flashlight being an item on the armor, than having to do the old duct tape mod is certainly nice lol It is a fairly clunky game though. I can go back to Half-Life 2 which released around the same time and it plays great. Good basic controls, movement is nice, but Doom 4 feels heavy handed and not in a gameplay way. It's not FEAR 1 bad where it feels like it plays like garbage, but I have trouble going back to kinda older shooter stuff. Would kill for some basic iron sights. I'm missing far too much with a shotgun than I really should. Also there are some texture stuff that looks alright and some looks like they came from a PS1 game. This is a 2004 game, by the way. I feel like they could've put a little more effort into that area.
I might play through it fully and it has Doom 1 and 2 on it also, but for 5 bucks, I can't honestly complain TOO much lol