The best game I have ever played!
This campaign is brilliant. The story line is great and even better when you download the Chapter 5 patch.
The game play is really fun; I haven't put this game down since I got it. The graphics are good for the psp too.
The game varies in difficulty, the bosses can be really difficult to defeat, but the other levels are quite easy, of course there are different difficulties. But the difficulty doesn't seem to vary between them that much.
In each level there are brief cases that you have to collect. When you collect enough of these, you will unlock the better weapons.
There are also challenges to complete, these unlock the upgrades (eg carry more grenades etc).
The one thing that I'm not a great fan of in this game is the controls of the vehicles. X to accelerate, triangle to reverse and the two shoulder buttons to move the turret or guns. This is my only slight problem with this awesome game.
Online (Combat zone)
This is also brilliant; you have to download a patch for it. I would say to anyone DOWNLOAD IT!
This game all in all is well worth what ever you pay for it. I love it. I'm going to hate the day I complete this game on the hard difficulty.