GI.net: "Metal Gear Solid: Portable Ops Plus is quite a mouthful, isn't it? Let's just go with MPO+ instead. MPO+ is a first-person shooter set in the mercenary underworld of South America in the early 1970s. This isn't just another run-and-gun shooter; the missions are stealthy, and a violent run-in with a couple of bad hombres at once can be permanently discouraging. In fact, stealth is such a major factor that you have a constant gauge monitoring the sound you're making as well as the sounds of nearby enemies, and an additional icon shows up (a chameleon!) when you're hidden from view.
MPO+ is based on the popular Metal Gear Solid: Portable Ops, but it's designed primarily for multiplayer gaming, which is why there is little or no plot to be found in it. The higher levels are (or at least seem to be, if they're not) completely random. There's no real story to the game - no way to justify your missions. You're simply going on mission after mission (called "infinity mission"), capturing or killing enemy troops across unpredictable, but similar, urban battlefields. Capturing them is much more rewarding since prisoners may end up joining your team!"