Quake 2 multiplayer is such a blast. The cat-and-mouse chase fights in that game is what defines the genre of "arena shooter" for me, there's still nothing else really like it.

The campaign has a place in my heart too, even if it's not perfect. A lot of DOOM's level design was predicated on claustrophobic interiors, and when you go "outside" in many levels it feels like a glorified courtyard. From the very first level, Quake 2 pushes hard to create an illusion of environmental complexity that plays very distinct from Quake 1 or DOOM.

Personally I think Unreal Tournament perfected the genre when it comes to multiplayer. Q1 was a lot of spamming of grenades and so on. Q2 was better. Still a lot of chaos. UT99 was also chaos but you could combine it with perfect moves and high precision shots. Great games all of them. I used to be an elite UT99 player but as the pace kept increasing along with my age my reaction time was simple not good enough anymore. Even if tactics compensated a lot those games are not like sneaking around in CS. I mostly played CTF. Good old times.