This is a ground-breaking game!
Enough of this tech b*****it... let's talk about the game itself. The graphics are OK, although you'll feel that everything lacks detail, especially if you compare them with 2.5D games like Duke Nukem 3D or Doom. The sound is great, and if you have no problems with constant CD-ROM access, you'll find that the soundtrack is amazingly creepy and it's perfect to bring a unique atmosphere.
The gameplay is the feature in focus, simply the best until Quake II's release. The game also offers a good replayability, allowing you to play highest levels of difficult (be aware that there're two secret ones). However, the greatest thing in Quake the multiplayer, which brings amazing on-line matches without any serious lags, especially when using a broadband connection.
The maps in Quake are well done, complex and with a lot of secret passages. The monsters are not the same as the ones in Quake II. You will face zombies, ghosts and some other creeps of undead nature. The weapons are rather simple, like the shotgun and the grenade launcher, but expect some bizarre stuff such as the nail gun and a bloody axe for melee encounters.
If you didn't try this game yet, don't waste your time and get yourself a copy. If you can stand the outdated graphics, you'll find plenty of chaotic action in Quake.