While Vaan and Penelo lacked something in the way of character development (Penelo definitely felt like she was thrown in), Vaan was there to offer a point of view of the main storyline of the game. All other characters had certain points of their past revealed in the game, so I don't see how they had some aspect of characterization.
Gambits were completely optional and anyone complaining about them has moot points, to be honest. I loved the Gambit system because of the monotony of grinding in the game. Also, it was awesome to actually set up the AI of your other two party members, rather than depend on general AI set-ups where they almost always screw something up somewhere along the line.
Of course, the best aspect of the game is the gameplay (hell, I put around 300 hours into the game). It was a fresh change from past FFs, which is something the series needed. There are few games that make me WANT to play through it three times in a row (regular playthrough, power playthrough and then a Vaan solo one), so that says something about it.
Also, people complaining about the lack of a "love" component need to look closer. There were some elements of it in the story, but it wasn't forced down the players' throats like it was in FFX. That was one of the things I hated about FFX; the love story was so prevalent and sickening, it made me not care about Yuna/Tidus.
