Jak II is a bad game. What Naughty Dog did, is decided to focus on the story more than anything. That's what they were selling, a 'mature', dark story in what shouldn't be called a platformer game. So to do this, they set Jak in this dystopian society, and because it's a dystopian society, things must be fucking awful, which Naughty Dog faithfully creates down to painfully bad level design and crappy game design in general.
Saying it's like GTA is doing a disservice to GTA. Even GTA IV, which had a pretty crappy city, still let you decide, for the most part, what routes you could take to get to any given destination. Not so in Jak II. There's one route and only one route to and from different areas on a map for the majority of the game. There's no shortuts. There's no variation. And it might not have been frustrating if it wasn't for the fact that sometimes you'd be ping-ponged back and forth across the map between two or three characters before accepting an actual mission, and each trip takes up about 5-10 minutes. There are cops that chase you, and it's not really that bad, but it gets annoying after a while, because like I said, the game only gives you so very few ways of getting away from them, and after a while they just become noise, instead of a useful, fun addition to the game.
And you'll be lucky if the mission you're sent on lets you do any platforming at all. I honestly can think of just three parts of the game that had a major amount. The majority of it relies on shooting, and the rest of the game is either half-assed skateboarding or racing (which isn't quite as half-assed. I'll grudgingly admit that the racing wasn't that bad). Fortunately, the very few platforming segments are well designed. Unfortunately, it feels like you're on a constant triforce hunt for everything inbetween until you get to one, except slightly worse, since it takes up most of the game.
So thanks to the new, dark, edgy story, we not only get a shitty city, but we get guns for the shooting segments, and there are four of them. I got this game the same time I bought Ratchet & Clank 2. My full expectations were that Jak II was going to be totally awesome and that R&C2 would be kinda average, just based on the first entries for both in their respective series. Playing R&C2 was a sort of revelation. Jak II added four guns and called it a day. R&C2 had a shitload of weapons, and they could upgrade as you played them, keeping the game fresh and fun. Jak II was by-the-numbers at its best by comparison.
There's also a dark Jak mode, and it doesn't really do anything good or bad. It's an extension of the different modes Jak could go into in the first game, but it always felt like a ploy to nab the early teen market that loved DBZ at the time.
People say it's a hard game, and I don't really see that. It wasn't easy, but it wasn't hard. I can only think of one section where I got stuck (it involves skateboarding above toxic water), but that was it. For a half-assed shooting game, the enemies have appropriately half-assed AI. So not even the majority of the actual game is fun.
So if Naughty Dog decided to ruin their own franchise for story, the story must be good, right? Of course not. Naughty Dog can barely design a GTA-lite city. They can't tell a story. There's this thing that starts to happen with a love triangle, and it's never mentioned past the 15-hour mark. The dialogue is particularly terrible, and every character is cliched in the worst way, down to the now-gruff-and-troubled lead character (the game starts off with Jak having been tortured for years. Fun!). What's kinda interesting to me is that they kill off their most interesting character halfway through the game. It's almost like they could tell he was somewhat likable and had to off him.
When it comes down to the boss battles, they're pure trash. The final boss battle is, in particular, one of the weakest in gaming history. You run around in a circle and shoot at it. That's it. That's no exaggeration, it's exactly what you do. You keep shooting and shooting until it dies from it. There's no strategy, no thought put into it at all.
Jak II is a terrible game on most accounts (being the story and gameplay and design in particular). The animation is pretty great, but you could also play a Ratchet & Clank game for good animation, and you'd get better level design, and something more fun in general.
And I guess this says just how lazy or clueless Naughty Dog became between 2001 and 2003: Jak II is a sequel to Jak and Daxter. In Jak II, you have travel the same routes over and over, without variation. Jak and Daxter had warp points. There are none in Jak II.