Here are some of my thoughts after playing a-lot of the single player.
If you are going to play the game make sure you turn on the Co Op story mode, it seems to be effortless to use so DO IT NOW! So far I have played with it on the entire time, and people can just jump it at any time, with that said I have had no issues with the games friendly AI; I can not say how much this feature rocks! The story was awful for me until I left Mantel, I think Free Radical did a good job of making the player dislike Mantel, Mantel soldiers, and Nector.
This game is not for the graphics whore's, this game is not for Gamers looking for the next AAA shooter, this game oozes average at best, and questionable at worst. You will find the weapons to be your standard affair, you have a riffle, pistol, shot-gun, Heavy Machine gun, Rockets, flame thrower, sniper rifle, grades, and they are not very unique or memorable weapons to use, but they get the job done and sound unique. The game also has some interesting gimmicks especially on the rebel side, these special attacks are not forced and it is up to the players to use these tricks against the AI (Nector bomb/Mine, play dead, Nector knife). Oh did mention you can invite people and see who is online in the game? All games need to have these basic PSN functions and its a god send!
The controls are tight and responsive, I did not have to change the default sensitivity, and I have to do that in most games, I did however turn off auto aim as it seems to affect the accuracy of my shots. With that said vehicular controls are OK, but could have been better; I can control them with ease (Looking at you HalfLife), but the levels I have used them in with one notable exception "The beach Level" have been frustrating because of there design!
All in all the game is just good, it has some frustrating level design, a very small amount of texture flickering (I have only seen this in the Mantel ships on the video screens), but rock solid frame rate and smooth level transitions.
Its a flawed and very average FPS, which counters simplistic friendly AI with well implemented four player jump/out Co-Op.