It's hard to think how much the graphics have improved, since Doom II was just released a year before Quake.
Gameplay
The gameplay, like I said, is very easy to pick up. You move, shoot, look around, and jump. Oh, and you go swimming sometimes. The controls are very simplified, so when you're a noobie the first time you play this, you will be mastering the controls at the end of your play.
You'll be in the heat of action and at the edge of your seat as you dodge out of the way of rockets, and sludge balls, and more. You'll have so much fun, and be in so much action, that the time will pass you by so quickly, you won't even have time to look at the clock. This game is perfect for when your friends are gone, you're alone at home, and you're just waiting for the day to end.
Graphics
What I have found so amazing about Quake, is that DOOM II was just released the previous year (1995). Just one year later we get a game looking like Quake. Wow. 'John Carmack magic' at it's finest.
You will even now be amazed that a 1996 game like this ever got close too looking how quake does.
You could tell that id Software really pused sprites out of the spotlight and brought raw 3d, fully animated, textured monsters and well...everything into the game! The graphics are insanely good.
If you disagree, remember...1996...yeah. Wow.
Sound
The sound in Quake was a revolution for the time, and its still quite good now.
You will hear monsters from afar coming at you, it really gets your nerves up as you frantically start looking around for some movement to fire at.
The guns and blast of carnage will keep you all hyped up. While there is no music in this game. It might have been for the greater good. You will have so much noise about you, that you won't need music.
The sound in Quake is stunning. Just like every aspect of this game.
Overall Quake is great in every aspect and makes a truly near-flawless game. There is also multiplayer action that is so amazingly fun, that you wont want to stop. If you don't already have Quake, it would be a recommendment for you to get it A.S.A.P. and see what you've been missing out on in the last decade.
Quake rules. Period.