Let me just say this. The beginning to this game is ultimate. There is no way it could have been better. There's now two cities and a huge desert. It is about four (my estimate) times bigger than haven city. And what's more, the sand actually acts like sand. If drive sideways along a dune, you'll find yourself slipping.
When you get called back to Haven City, it is amazing. Everything has changed. One section is only rubble, one section has been consumed by the Metal Heads and one section has been done over entirely. Everywhere you go you will see Blue Guards battling Red Robots battling Metal Heads. Tor gives you a whole bunch of quests to help your side win.
However, the rest of the game was not to the same standard. Nothing was really developed as much as Jak II. The new characters only appear briefly as well as the old. The end approaches way too fast and the replay value is a lot less than the previous title.
Last thing. I think the creators could learn a lot from Ratchet and Clank. Not graphics or story wise but gameplay. Having no strafing is frustrating.