Not only one of the best PS2 games, but also one of the best free-roam/adventure/shooter/platformer games to date.
Jak 2 took many of the things Jak and Daxter did right and improved them drastically. The platforming is really smooth, the areas are well designed and detailed. The shooting elements were a great addition to the series as Jak also gets a new voice and no-nonsense attitude. I admit that the first time I heard Jak speak I was a little thrown off, but I grew to love the dialogue between him, Daxter, and all the other characters in the game. The other addition I found interesting was the introduction of Dark Eco powers as Jak becomes a one hit killing machine practically, especially with the always awesome looking Dark Eco Bomb.
The best addition, in my opinion, was the addition of a massive over world with subareas for missions and the transportation included. I admit that I'm normally not a big fan of large cities with subareas (GTA inspired style), yet Jak 2 does well by making the city seem small at first since most of it is blocked off and allows you to enter more parts. This feature is nice as it eases you into the traveling and navigation of the city, which by the end of the game you could do with your eyes closed (literally).
Overall, the game works well with the only issue being that the difficulty seems to be almost too easy at times since there is almost no penalty for dying except being forced to redo parts of an area. Yet as that is the case, it makes a good intro game for anyone looking to get into video games with the comedic dialogue, great visuals, and excellent gameplay. If you haven't played this game yet, do...now.