If you like Prey and Doom3 then you'll probally like this game + it has a good multiplayer. However it's pretty linear..
Doom3 - Old school Doom action with a storyline focusing more on horror.
Quake 4 - Picks up from Quake 2 and is more war/action focused with alot of fighting with you npc's
Prey - Again a step up from the previous 2 games with some kool new features and is about aliens. Its more about puzzles and close combat.
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This game was the 3rd i played and it seems a slight step back in terms of graphics and optimization to Prey but its pretty close anyways. The gameplay also felt more dated than Prey and more "old School" and the single player doesn't seem as satifying than the other 2 games.
However the Single player is a good length, slightly shorter than the other 2 and theres ALOT more action and more enemies coming to you at once. It's going to be real fun to you if you liked the other 2 games but don't bother if you didn't.
The guns are also like the other 2 games and so they arn't really that great compared to other FPS games. However this didn't really effect my fun but in a FPS guns are quite important.
It's a simple run about shoot anything that moves FPS with no strat or messing about really and there are some puzzles but they take about 5 seconds to work out so not that hard.
The Graphics i felt wern't as good in terms of polish to Doom3 and Prey and i didn't really like some weird blocky looking scenery like it came outta HL and the picture backgrounds are also pretty bad. The performance is also a mystery to me, like why does the game use much more memory than the other 2 games and runs my 2gb ram dry on ultra.
The sounds are pretty much like the other games and arn't the highlight of the game however they aint bad.
The value depends on if you enjoy the Multiplayer which is basically Quake 3 with new graphics. However theres not many people that are playing it and UT04 seems like the better option to go for. I guess they wanted their Multiplayer to go onto the game "Quake Wars" which is justa multiplayer game to take the fight back to UT and BF games that have outshined Quake since 2001.
So overall its a pretty basic game that lasts in the single player between 6-10 hours and has a pretty kool multiplayer. If you liked Doom3 and Prey then you'll love more of the same, otherwise stay clear.
+ I also found Prey and Doom3 to have kool little extras like radio station phone ins you could listen to and PDA messages you can read but this game seems to be missing all that kool stuff.