Unlike many other games for PSP, Field Commander seems like it was designed specifically to take advantage of this system's portable form factor. The fact that Field Commander is a turn-based military strategy game lends a lot to that fit, but it's also a game that easily stands on its own merits. Its fully 3D units and maps lend some amount of flash to the proceedings, but you'll find that the visuals are actually the weakest component of this well-balanced strategy game, which offers awesome value even outside of its engaging single-player campaign.
Field Commander's design is based around maps divided into squares of varying terrain types. Different types of terrain afford different bonuses or penalties to defense and movement. For example, mountains offer a high defensive bonus for units moving through them, but only air and infantry can traverse that type of terrain. Swamps have a defensive penalty and are impassable by wheeled vehicles, and they also slow tracked vehicles to a crawl. There are usually several key points of interest on Field Commander's wide variety of maps, including cities for generating income, factories and airports to pump out units, and special control rooms that allow the periodic use of a devastating attack. These control rooms are particularly interesting, letting you unleash attacks like air strikes to damage all units in a line, or a napalm strike that hits on a specific spot and then spawns a ring of fire around the epicenter that grows for a few turns, burning any forest and damaging any units caught in the blaze.
Many of the typical conventions of turn-based military games of this type are in full effect as far as the terrain goes. You can park vehicles on enemy-controlled factories to block the production of units, for example. But you'll also find that Field Commander offers fairly unique quirks of its own, like the ability for an air unit to occupy the same square as a land unit or ship. Perhaps what's more interesting is that terrain can be deformed by tank cannons and other explosive attacks. For example, you can command a tank to fire at a patch of dense forest and thin it out into a lightly wooded area. What was once passable only to infantry can then be traversed by vehicles. You can even shell an enemy-controlled "dense city" and reduce it to a smaller city type, which will diminish the income of your opponent. These types of tactics figure heavily into Field Commander's rich gameplay, as you can weigh the benefits and drawbacks of thinning out a dense forest to open up a second front of combat on a map.
Field Commander's units run the usual gamut of land, sea, and air units for games of this type. You'll control everything from standard infantry grunts to swift scout cycles to different types of tanks, helicopter gunships, battleships and submarines, and more. One of the more interesting units in the game is the special-ops commando. Armed with both a rifle and a mortar, special-ops commandos can effectively fight infantry up close, or hit vehicles from a distance. They can also lay mines on the battlefield, which is great for blocking off choke points like bridges. While all these abilities make it sound overpowered, the unit is still very fragile up close--so any vehicles that can get inside its minimum mortar range have no trouble tearing commandos to shreds. There are also some interesting vehicles too, like stealth tanks, which can go into camouflaged mode at the expense of greater fuel consumption. Their cannon is especially devastating to vehicles when it attacks while cloaked. There are also equivalent infantry and aircraft in the sniper and stealth fighter units.