If you liked Doom 3, or if you love First Person Shooters, you are gonna love Quake 4.
Campaign- Quake 4 has a rather long campaign, compared to other first person shooters. Playing Quake 4's campaign can take you between 8 to 15 hours, depending on your skill level and the difficulty you are playing. Like all Quake games, there isnt much of a story, but there is enough story to keep you slightly entertained. If you have played Quake II, you will understand the whole setting of the game, as Quake 4 is set on the alien world of Stroggos, and your main goal is to take down communication systems and such. But the real core of the game comes from shooting a bunch of different aliens. There is a large variety of guns to choose from, and it is very enjoyable to kill some Strogg.
Graphics- Although the graphics are not nearly as good as graphics can be now, they are actually quite good, and textures are detailed as well as blood splatters and explosions.
Gameplay- Gameplay is pretty much a standard science fiction first person shooter, but still, shotting aliens is always fun, especially when you have a ton of weapons to choose from. Your machine gun has a flashlight mounted to it, so you will be using it a lot, as this game can be dark at times. There are also vehicles in the game, which are fun, but walking around in the dark is still more enjoyable.
Multiplayer- There aren't very many people online anymore, but you should still be able to find a game to join. Multiplayer is very much like Quake 3 Arena, just with updated maps and graphics. Multiplayer is fast paced, so get ready for some speedy fraggin. You can also play via LAN with a friend.
Overall, Quake 4 is an excellent PC game you simply must at least try out. It is very affordable these days, try looking on Amazon or eBay, or borrow it from a friend. If you are a fan of the Doom series, Quake series, or first person shooters in general, you will enjoy Quake 4.