Better than you'll expect..
From the first mission until the end, its an outstanding game... each mission has many memorable moments to keep you coming back for more. I have played the first mission 10+ times and still love it.
The best part of the game part of the game for me would have to be the particle effects from shooting the crap out of everything. Honestly, I could never tire of this. The graphics are stunning, even on the ps2, the environments, guns, everything. I was expecting a bit of slowdown, but to my suprise I have not seen one hint of it.
The game may be a little to short, could have done with a couple more levels, but the levels you get are excellent.
At the end of the day, if you love guns, love shooting stuff just for the hell of it.... this game is for you!