There are a few PSP games that are as fun as this, with a little sharp edges here and there...

User Rating: 8.5 | Undead Knights PSP
Undead Knights is in a league of it's own. Not as spectacular visually as expected, but the gameplay more than makes up for the lack of visual presentation. There is also a lack of playable characters, but each character has an arsenal of moves enough for the player to want to try every single one. One of the coolest features of this game is its premise of being able to transform enemies into your own personal zombie warriors, a cool feature that slightly disappoints because of its limitations, a limitation of 12 zombie knights, any more and it instantly dies. But what makes up for this limitation is the ability to turn "Executioners" into your Zombie warriors as well, and trust me, big zombies under your control is just plain awesome. So to break it down...

The Good:
Unique gameplay, GORY(in a good way), intriguing story, interesting characters and the ability to turn enemies into personal zombie warriors, including the big ones.

The Bad:
Lack of visual presentation, limited number of zombie soldiers (12) and lack of playable characters.

All in all, this game is really good, don't rent it, GET IT, because it is as fun as it promised it would be.