I've always been familiar with Quake, but only as a multiplayer game. I've played a lot of arena shooters (I'm more of an Unreal Tournament fan), but for whatever reason I never got around to playing the real Quake. I didn't really expect much considering how badly DOOM has aged, especially in terms of level design and general game feel, but I was really impressed.
Quake holds up on all fronts. The gunplay feels good, the movement feels great, the enemy variety is pretty good, and the level design is a night and day difference from DOOM and DOOM 2. It's hard to imagine that they came out only two years apart.
Despite being copied a million times, I feel like Quake holds its own against modern shooters. I would recommend it to anyone who likes movement shooters, and I probably should've played this ages ago.
P.S: I HATE SHAMBLERS I HATE SHAMBLERS I HATE SHAMBLERS
RotT has really fun weapons and a banging soundtrack, I can see how that would be the defining FPS of the time for some people. I think my favourite FPS of the 90's was Blood, they nailed the atmosphere in that game.