Lethal Alliance is an OK action game. Far from great, but not bad. The best thing you can say about it is that it manages to have a movement/camera system that actually works pretty well within the confines of the PSP controls, something that a lot of other 3D action games on the system never really figured out. But it's basically the over-the-shoulder equivalent of a "corridor-shooter" FPS, just a bunch of levels that consist of mostly linear hallways full of repetitive blasting of the same enemy goon models.
The game is set just before Episodes IV-VI and ties in with the whole Kyle Katarn storyline from the Dark Forces/Jedi Knight games. You play as a Twi'lek mercenary who Kyle apparently is lazily subcontracting a bunch of his work out to. She's really a little OP, jumping and flipping around like Raiden from Metal Gear Solid 2 and basically seeming to have the ability levels of a Jedi. After a couple of levels, you also get a little floating droid buddy who is needed for computer hacking, can be chucked at enemies to stun them for a bit, eventually gets the ability to block blaster fire, and also pulls double duty as a vehicle/platform in certain level segments.
The game's marketing made noises about "stealth" and varied modes of play, but this is basically just window dressing. 90% of the game is running through corridors blasting whoever pops out at you, interspersed with the occasional annoying turret sequence or having to use your droid to do a little platform-jumping up a shaft of some sort. The "stealth" element is simply that once in a while, you walk into a room and one or two dudes have their back to you, and you can walk up behind them for an auto-kill animation with your little laser knife thing. You do get a "stealth camo" ability late in the game but it's employed in a cursory way -- this is a shootfest first and foremost with a dash of Tomb Raider scripted hotspot jumping every once in a while.
The handful of other alternate gameplay sequences involve your droid. Once in a while he needs to go into some air vents to disable security, which consists only of dodging laser grids (why are they set up to move around and turn on/off? Why not just leave them on permanently?) and little jihadist exploding sentry robot things. There's also an occasional level where he's used as a vehicle to fly outside as you hang on for dear life dodging obstacles and cars.
The camera and targeting system at least works decently well, if not perfectly. When no enemies are about, you use L and R to rotate the camera, and areas are sensibly designed so that you rarely need to look up or down for any reason. When enemies are about, you start targeting them automatically, and L and R flips between them in the directions they are currently relative to you. The only place this kinda goes awry is in rooms where you also have to target a computer to send your droid buddy to hack it, as the system can be flaky about whether or not it wants to target these.
The game was aimed at a casual audience as it is very much on the easy side, and you'll probably breeze right through it. It's not the most inspired use of the Star Wars license, but far from the most terrible/boring either. If you've got a Twi'lek thing or just REALLY have to see every aspect of the Kyle Katarn plotline you might find it worth a few bucks to pick up.