When I played Quake 4, I discovered a second disc in the game, which featured Quake 2. Out of curiousity of trying, I have to say I loved Quake 2 more than Quake 4!
As a person who's been playing old school first-person shooters since Duke Nukem 3D. It is horribly addicting, fast paced, intense, and overall fun! Like a Typical FPS before Half-Life 1, it was a satisfyingly ultra-violent game where you take down cyborg aliens know as the strogg, and given lots of weapons and kill them however you want. Each weapon has a pros and cons. For example, the BFG 10k is a devastating weapon, but could hurt you if you are too close and consumes lots of ammunition.
In the story, you are BItterman, a soldier from earth invading Stroggos to destroy the Stroggs invading humanity and prevent them from turning humanity into cybernetic slaves. While landing with the army, you got hit by a cowboy, and you land somewhere else. Thankfully getting hit saved you when all the soldiers were pinned KIA or MIA.
Also, thanks to steam, we still have a dedicated audience of multiplayer to this game! Like the single player game. Super addicting! All I can say about the Multiplayer, it is a total blast with deathmatch, team deathmatch, Capture The Flag, and so many other modes! Especially Co-Op!
Also, try to find the Ultimate Quake Patch for the soundtrack! Sonic Mayhem has made the best soundtrack for the Quake series.
Amazing game, get it!