Most fun I've had in a story driven FPS since the half-life series. Run and gunning that doesn't get old.
This game is pretty short, and I beat it in around 10 hours. I think that's a pretty good length for such a fast paced game. Doom 3 was twice as long but that game felt like it dragged on longer than it should have and got pretty boring. Quake 4 is a game you can and probably will power through in under a week.
-There are countless triggered animations which are so nice to watch. Examples are the vast number of elaborate bridges constructing themselves before your eyes, and the cut-scenes that involve and foreshadow your boss fights. The devs went out of their way to make these moments truly memorable.
-All the guns are satisfying and FUN to use. And there's enough ammo scattered around that you will be using all your weapons. You won't have a single 'backup' weapon that's only used for the fodder because each weapon has its advantages (asides from the pistol which you will never use)
-There are no frustrating puzzles, and the way the maps are made make it so you won't easily get lost. You don't need to think about where you're going so much, and can enjoy the constant run and gunning as you head towards each objective.
-Regular characters will accompany you and come and go, some of them surviving the game while others die. This accompanied with the frequent comm chatter make you feel engrossed in your role, and in the game.
-Probably the multiplayer, but my rating ignored any aspect of this games multiplayer because I didn't get this game for the multiplayer aspect.
-Vehicle levels are not up to par with on foot levels. Luckily they don't last long and they are few and far between.
This game still looks great today, despite the somewhat dated engine. It's an appropriate length and is a fun ride the whole way through. If you like this type of game I see no reason why you shouldn't pick it up.