Good, but a few bugs and glitches prevent it from being as good as the PS3 port *spoilers follow*
1) There's a scene in Jak 2, where Kor reveals himself to be the metal-head leader, and his face is blacked out. This is the same as in the PS3 port, leading me to believe this is a port of a port
2) The rear touch-screen is over-used. Rather too many features, without any clear in-game instructions as to how it's used properly (In Jak 2 I found myself transforming into Dark Jak by accident)
3) There is an issue with frame-rates, whilst it rarely gets in the way, it can be a little annoying, really obvious when facing large waves of enemies
4) There seems to be an issue with grinding where at the end of a rail, you're shoved to the right for no reason, this hampered my on several attempts of certain levels
None-the-less this is a great game, and a recommended game for Vita Owners who are Jak and Daxter fans