Junpei is an incredibly multi-dimensional character. The fact that you just dismiss him as an asshole makes me wonder whether you played much of the game at all. I'll admit, I really didn't like him when I first started playing the game; he seemed like just the token comic-relief character and indeed a bit of an asshole to boot. The little falling out he has with the main character early on certainly didn't help his case. But then he apologizes and eventually you actually start to get to know him and his actions make sense. Then the whole Chidori arc happens and he becomes one of the best video game characters ever, in my opinion. He's not perfect. He's a struggling teenager, with a bit of an inferiority complex, but he turns out to be a brave friend.jhoroz said:Junpei is an envious asshole and Yukari a self centered whiny *****. There is absolutely very little likeable about the P3 cast.
In general, while most of the Persona 4 cast was immediately likeable, I didn't feel as close to them, like I "knew" them as well, by the end of the game as I did with Persona 3. I really felt this bond with my party that no other game has quite given me before or since. And the female route of P3P accomplishes this even better since you can form Social Links with all your party members if you choose, not just the girls.
As for the OP, I would very strongly recommend playing Persona 3 before 4, if only so you don't get caught up on the technical downgrade by going "backwards" through the series.