Ratchet & Clank: Size Matters is, in my opinion, the best platformer on the PSP. Size Matters packs all the fun, humor, and ridiculous weaponry of its PS2 counterparts into a portable package. Developed by High Impact Games, chiefly composed of former Insomniac employees, its pedigree shows.
Once again thrust into the fuzzy role of Lombax protagonist Ratchet, you find him and robotic sidekick Clank taking a well earned vacation. Before long, however, the duo are tasked with saving a kidnapped little girl and uncovering the secrets of the mysterious Technomite race. The story is relatively simple, but keeps the pace moving throughout the adventure. The writing and voice acting are extremely smart, however, and filled with the series' trademark humor.
Size Matters takes full advantage of the PSP's capabilities, producing visuals that rival (and often exceed) those of its Playstation 2 prequels. Character models are detailed and animate fluidly, and bright weapon effects and explosions illuminate the screen. Soundwise, you have solid voice acting and an upbeat, spacey score.
Gameplay wise, the game is more similar to the earlier entries in the series, with more emphasis on platforming than shooting, although there is still plenty of the latter. It is a good thing the controls are rock-solid. Very rarely will you find yourself performing an action that you didn't mean to. Only aiming at distant enemies with a long-range weapon poses any difficulty.
For fans of the series or just platformers in general, Ratchet & Clank: Size Matters is great fun. Excellent graphics and sound, combined with familiar and fun gameplay make for a potent combination. Recommended.