I certainly knew what to expect from Quake 4, having Doom 3 in mind, and it did all that very predictable-like.
In a retrospective view, i see Quake 4 as a success and as a true worthy sequel to Quake 2. It packs up a long and in-depth single player campaign, that is now certainly more developed than in Quake 2, since it adds more animation, cut scenes, dialogues, additional objectives, and is not so generic in general. Also Quake 4 borrows elements of horror from Doom 3, improves the complexity of fighting by upgrading the AI of the monsters and adds some new gameplay elements like vehicle control. On the bad side, since it is based on the lame Doom 3 engine, it lacks all that great pace and free movement that Quake 2 had - it is a major failure in my eyes. Also because of the same lame engine you will find yourself in situations where you won't be able to escape or move being surrounded by monsters - another example of how bad Doom 3 engine is compared to Quake 2. Another major drawback is no cooperative!!! You might say that Quake 4 is too complex for coop as it's campaign concentrates too much on it's main protagonist, but i say BS.. I rather have a decreased dialogue, than have no coop.
Now when compared to Doom 3, Quake 4 certainly improves lots of things - most important is that at least some of it's weapons have a fucing flashlight now.. No comments.. There are minor improvements in the details, animations and the AI of the monsters - good. Added are episodes where you get to use some machines or vehicles, also added are episodes where you are finally not alone and other marines accompany you, and most important Quake 4 makes you feel like there is a balance between the Strogg and the marines, and that there is always action somewhere, while in Doom 3 it was so ridiculous that all of the base marines have been slaughtered like puppies, and you somehow were the exceptionally gifted one to single-handedly pwn every monster in your way with ease.. Despite all those improvements there is one thing missing from Doom 3 - no longer Quake 4 gives you that "wow" feeling, because everything has been seen and done in Doom 3. Quake 4 looks almost exactly as Doom 3, and feels that way too often, and although Quake 4 has some moments of horror, nowhere it comes close the match up Doom 3 atmospheric intensity.
Multiplayer in Quake 4 makes no sense - without any doubt it is the worst multiplayer in all of the Quake games - it is so slow and has so little potential to develop skill in it, that is almost atrocious to call it the next big game. Compared to other FPS games, Quake 4 multiplayer is actually good - certainly easy to get used to it, and is quite competitive, but nowhere as solid as Quake 2. Basically there is a pattern now in all of the Quake games, that the newer the Quake game is released, the slower and less competitive it's mutliplayer is.
Quake 4 is a good game for the sake, that it's campaign is entertaining and has some improved gameplay elements from Doom 3, but eventually Quake 4 does not have the level of impact and atmosphere that put Doom 3 in the first place, so i can not rate it higher than Doom 3.