I've put about eight hours into this game and I have to say it's the best PSP game I've played to date. I haven't played the prequel on the PS3, so I'm looking at this game through new eyes, but it does seem to be the type of game better suited for the PSP. I only have two gripes with the game so far: one is that all of the missions you get for the month (you get new missions each month, each month is sort of like a new chapter or level) are on the same maps. I've done a bunch of missions and a lot of them are on the same area, once you know where the enemies are going to be, the game isn't too hard. Which brings me to my second gripe.
The game is too easy so far, I've heard it gets harder later on, but right now I really haven't had any trouble beating anyone and I'm playing on normal (can only imagine what easy would be like). I've had a few soldiers die on me, but it wasn't because I was actually beaten or conquered by the opposition, it was because I tried to sneak past a tank and it didn't work out too well.