Jak 2 is by far, in my opinion, the best Jak game ever made.
A friend of my father first showed me Jak & Daxter when it was on the PS2, and I didn't really "enjoy" it, but it was a decent game for me at that time, a few months or years later he told me that he had Jak 2, and I didn't even finished Jak & Daxter, so I went to his place with very low expectatives, and when I played it, I have to say that, to date, it is one of the best games I have ever played, even better than any game of my beloved Ratchet & Clank franchise, and Jak 3 was a good one as well.
So it comes to which genre you like, Jak & Daxter is a decently-done platformer (not as good as Crash Bandicoot or Sly Cooper though) and Jak 2 and 3 are more like an open world weapon-based combat game (not as refined as Ratchet & Clank's combat play), but they all are great games in my opinion.
I can't say the same about The Lost Frontier.
