My brother was a huge fan of the games, and we have all the original 3. I had no idea more had been made until just recently, but apparently they shouldn't be very good, so reckon I haven't missed out on it that much.
Personally, I've only ever finished the first Jak and Daxter game, and it's still my favourite out of the entire series. I enjoyed both 2 and 3, but I've always been too much of a noob to finish those two ;D And I honestly kinda feel like both of those two strayed away from what made the first one my favourite. I mean, it was entirely about platforming, but I reckon since that was a bit of a dying genre, they moved into new territory to still keep the games fresh and interesting. And it actually felt like with each new game they gave it a new sub-genre to say. First one was entirely platforming, second one added shooting elements, and the third one added cars and races. And it's actually a pretty good idea. But I still feel like the games went too far away from the platforming, and that's also a bit of the reason to why I haven't finished the two, because I just couldn't keep myself entertained enough with the shooting.
The story though is what kept me coming back to the two others. While I liked the story from the first one, it got sooo much more interesting in the second one, and the layers 2 and 3 added to the original was just pretty awesome. I feel like they in general just introduced waay too many unnecessary characters though, who were either built up to more, or whom we didn't even get any information about, though the main culprit of this was actually the first one.
In any case, I like the games, and I still enjoy playing them every once in a while :D