Couldn't live up to the enormous hype.
Quake was a marvelous tech demo. The graphics were true 3D, and the multiplayer component was (apparently, I really don't know firsthand) revolutionary in its day, as one could easily hop on and find opponents through that direct TCP/IP thingie everyone was ooohhing and ahhhing over.
The single player game just wasn't all that compelling after the intense, Mars-meets-Hell action of Doom and Doom II. Plus, Quake set a new low bar for storytelling--there is no story, period. I haven't really played multiplayer Quake, and the idea of trigger-happy FPS fragging online just hasn't ever appealled to me, so I can't bury or praise Quake on that score.
The graphics are not now, nor were they ever, as impressive as they were alleged to be. YES, it was true 3D and used polygons instead of sprites, but that doesn't mean it was pretty to look at. The bad guys tend to look polygonal, which just doesn't cut it for me; I'll take good-looking sprites over jagged blobs any day. Not to mention how utterly BROWN the whole thing is…ick!
Quake's claim to greatness has to be that it paved the way for later games that were both technically brilliant AND aesthetically pleasing. Sorry Mr. Romero, but I just don't think design was law in this case.
The Bottom Line
Quake was a fabulous tech demo, but only a decent game. A "classic" in its brief heyday, it's just "ok" now.