Just finished Jak 3 and got the platinum on it.
The game was SO much better than the second, the story was really good, but the "twist" wasn't quite as great as in the second, but it was still really good, the only thing I disliked was that some of the missions were still extremely hard and got me pretty angry (Which is VERY RARE!) because the AI was just terrible and cheap and things happened that shouldn't have!
Example: Having to roll under an electric beam, I rolled under it, walked away, and a second later, when I was in the next room, Jak starts spazzing out as if he'd been shocked... and his health would go down, and I'm like what the fuck how is that even possible... Then there's another time, I was jumping between platforms, and I was backtracking so I KNEW I could go that way, and between two of them, an invisible wall appears... not fun whatsoever! And as for the annoying as fuck AI, on the mission where you go out into the desert to collect artifacts for the second time, it gives you like 20-30 seconds to get to each one, but it doesn't tell you that there's like 10-15 other cars all crashing into you and shooting you and knocking you off course... so god damn fustrating indeed!
Also, the last boss was a little TOO easy, because after each round you could refill on light eco and heal yourself to full... although the section before the boss (Where you're chasing it in the desert and it's like REALLY big) was pretty cool...
Story wise, Jak II + 3 are tons better than Jak and Daxter, but in terms of actual fun, the first game is miles ahead in my opinion...