Star Wars: Renegade Squadron.
I got this because I loved the Battlefront games on the Xbox, but converting them to the PSP really wasn't a great idea.
The control scheme relies on a lockon feature, which sometimes switches targets without you wanting it to. When you're up against a large number of enemies, this can quickly get you killed. It doesn't help that your allies hate you and refuse to work with you in any way, shape or from. They'll even leap in front of a laser blast aimed at a stormtrooper in order to annoy you.
Also, the enemy AI in the land battles is really inconsistent. After doing everything they can to stop you completing one objective, they'll suddenly get bored and wander off, leaving you free to complete the next objective without having to fire a shot.
The space battles make up for this to some extent, especially when things get a bit crowded, but they're nowhere near good enough to make the game worthwhile. Oh, and the scrolling text at the beginning makes the Phantom Menace introduction seem thrilling.
Star Wars Battlefront belongs on a PC or home console, the PSP simply can't do it justice. I have no intention of trying Elite Squadron after this.