Retribution acts as a side story that takes place between the first two PS3 games, though there's no Nathan Hale to be seen here. You play as James Grayson, a hardened former war hero who went rogue--and a little nuts--after the Chimera converted his brother to their monstrous ranks. Grayson was court-martialed and sentenced to die for his actions, but is pulled from death row by a mercenary group called the Maquis to act as a one-man wrecking crew, undermining the Chimeran empire in Europe. Grayson basically sounds and acts like Jason Statham, and his salty, sarcastic interactions with the other members of the resistance movement are often well-written and funny. You won't get much clarity on Resistance 2's nebulous storyline, but the game does offer a couple of interesting twists and gives you a close-up look at the nasty business the Chimera are getting up to, behind the scenes.
Veterans of the PSP Syphon Filter games will instantly recognize the two control configurations in Retribution. You can use the analog stick to move and the face buttons to aim, or vice versa, and both options work equally well. The one you choose is really just a matter of taste. The most crucial aspect of Retribution's playability is its helpful auto-aim feature, which automatically targets enemies that are even only sort of close to the center of the screen. You might think such generous assistance would make the game too easy; on the contrary, it merely saves you from having to pull off precise aiming with the PSP's imprecise controls, a feat Bend must have realized would tax even the most skilled players' patience.
Retribution is hard enough, anyway. The game throws more and more tough enemies at you over the course of its lengthy campaign, so even with the auto-aim, you need deft reflexes to manage the onslaught. There's also a cover system that makes you automatically take cover just by running up to a flat surface, so avoiding attacks and trading fire with Chimeran grunts and larger enemies, like Titans, is generally a streamlined process. You've also got a healthy arsenal of weapons in the Resistance vein, from the Auger, which shoots through walls and can generate an energy field, to the Fareye, the sniper rifle that slows down time when you zoom in on your target. All the weapons have a secondary fire mode, so there's some variety and strategy in knowing which weapons to use when.
Lastly, there's a bunch of extra content you can only access if you own a PlayStation 3 and a copy of Resistance 2. You can "infect" your PSP by connecting it to the PS3 and game, which also infects Grayson with the Chimeran virus and changes some minor aspects of the storyline. In gameplay terms, this lets him regenerate his health and breathe underwater, and (inexplicably) gives him access to a few powerful new weapons you can't get any other way. These additions make this tough game a little more enjoyable, and locking them up behind this ownership requirement seems like a shameless way to exploit the idea of handheld-to-console connectivity by selling you more stuff you may not already have.
My initial response to this arrangement was one of outrage, since you only need the PSP connected long enough to confirm you own both games before you get to use the "infected" stuff. But the good news is, Retribution is still a great-looking, fully playable shooter even if you don't own a PlayStation 3. If you're already set up to access the extra content, think of that as a nice bonus, but don't feel like you have to run out and get Resistance 2 just to enjoy Retribution. Based on the PSP's library to date, it's clearly not easy to design a good, console-style shooter on the platform, and so far Retribution is one of the better ones.