Metal Gear Solid Portable Ops + a good multiplayer, but single player "infnity mode" is not it's main focus.
If you have internet then multiplayer is where this game shines. Playing with people over the internet trying to be the best player in the world is what you'll be doing most of the time. If not, then you may have just wasted 20 good dollars, my friend, as infinity mode is it's weak spot. No story, no boss, no metal gear, nothing but knocking out troops and draging them to the truck to "persuade" them to join, a few new unlockable characters and the never-ending satisfaction of continually hearing the cries off your enemies as put a bullet in their heads.
Infinity mode is basically training and unlocking troops for multiplayer,which means hours of boredom for those with no internet acces and no friends. How many people you kill, the time limit, high score, none of that is recorded, except how often you beat it(No bragging to how fast you beat extreme mode).
The troops you pput in technical, medical and Spy unit don't do much, if anything. I think that is just for leveling up the extra troops. And even then, those areas fill up and in the end you eventually have 200 troops and only actually use the 50 or so units in t,m,&s units and the stealth units(the people you control)
So, in conclusion, If you want this game, by all means get it. Just don't expect much if you have no friends who are getting it too, like me.