Certain controls just don't work as well on the PSP. The system has long since accepted it's inability to fire weapons accurately, but we've seen top down shooters that perform much better than this. Since you can only fire in the direction you're running/facing, you'd best equip some kind of auto targeting item or up your critical hits stats. At least if you want to make it through this infested spacecraft with any ammo. It can't hold a candle to the roving reticule found on the Wii, but fortunately, the Melee combos fare much better with buttons.
The PSP's small screen does a lot to mask the pitiful graphics of the Wii version. But as passable as the visuals are on the portable, they're largely bland and lifeless with enemies just as repetitive and uninspired as the level design. A little more variety and intelligence in the enemies could've saved this shallow shooter, but alas, the fast paced action quickly devolves into yawn inducing tedium.