Well, as a massive Kiros fan, I have to say that Kiros deserved more. Same goes for Ward, who I believe the creators turned him mute just so they didn't had to come up with more dialogue. And even Fujin and Raijin, as they are my favorite duo, I really like them.
Aside from that, Squall's character gets a bit ruined with the romance stuff (which is the last thing for which I play a FF game, even tho the main theme of FFVIII is love); Zell has a side-quest, but it is only for you get a girlfriend to him, it is not very important (at least to me), and even without it, Zell has a good amount of development in my eyes. Quistis.... ehhhh...... well, she's there, I guess. Seifer has just enough, and imo Rinoa has almost too much, but she is the love interest, so I guess it is suppost to be like that. As for Irvine and Selphie, I do think they could get a bit more, but have a pretty decent amount of development imo.
As a not very big fan of Laguna, he gets a bit too much development imo, but again, he is Squall's father and a secondary leader, so I guess it is suppost to be like that. Raine and Julia could get a bit more, so could Ellone. Edea, I think has just the perfect amount of development, and Cid.... well..... he is there to give us the Magic Lamp and be an idiot for the rest of the game, I guess. I mean, even Biggs and Wedge get more development than Cid.
