A big game in a little package.
Love it or hate it, much of the PSP catalog consists of portable versions of console games you've already played. Many of these are faithful, spirited copies of their source material, but they are still copies nonetheless with a nagging sense of deja vu. Resistance: Retribution follows this pattern, but it's hard not to be impressed by how well-made this game is and how much the developers have crammed into Resistance's PSP incarnation.
A lengthy single-player campaign offers an satisfying parallel story in the Resistance universe. You'll be stomping through Europe in imaginative level designs, blasting away hordes of beasties with a fun assortment of guns and their respective alt-fires. Gameplay concessions are made to ensure the game is easy to play on the small screen. Generous auto-aiming makes some combat a bit trivial, though certain monsters are much easier to take out using manual zoom. Cover is handled extremely well. Sticking to objects is effortless, and popping out for bursts of fire is handled seamlessly. Tons of unlockable skills and perks make for worthwhile replayability if you're so inclined.
I didn't try out Retribution's multiplayer, but it's garnered solid reviews.