Great storyline, old school multiplayer from what I played, definitely better than previous quakes
Sound is perfect as well as presentation - there's plenty of bombs going off around you, and lighting is excellent. The weapon sounds are stunning, and the voices sound professionally done, but I won't give away any lines I found pretty funny. Special effects are near perfect, and if you have not seen the D3 engine in action you will surely be dropping a few pellets from your bottom.
Also, those dissapointed with Doom 3's gameplay will feel much better and finally stop whining. You fight along with your soldiers to take down the enemy strogg, and sometimes you can chat(well, barely). You fight in wide open spaces and even pilot vehicles.
Multiplayer--- well, I was never really a fan of Q3 multiplayer, so i guess my rating wouldn't be fair.
Quake 4 is definately a huge step forward from previous quakes, and the replay value was pretty heavy for me (DON'T FORGET ABOUT MODS).