I just picked up Metal Gear Solid Portable Ops and I'm enjoying it quite a bit. I've played both MGS Acid and Acid 2, which both have widly different gameplay (which I enjoyed and not many people around me did).

PO is pretty nice, although the controls are somewhat wonky. I really liked the control scheme for Syhpon Filter: Dark Mirror, and so far it's the game by which all other PSP FPSs are judged. I gave up on trying different setups in PO and am using the default scheme which is not ideal but still manageaable.

The recruiting mechanism is very cool. Having my own virtual army is lots of fun!

I plan on spending many many hours with this one.