What is your take on the Kingdom Hearts series?

This is a really vague question, but I was just wondering your opinion on the series as a whole. I've played them all and I adore them, mostly for the compelling story lines. What are your favorite characters? What are your favorite worlds? Which trio do you like the best: Axel, Roxas and Xion, Sora, Riku, and Kairi, or Terra, Aqua, and Ventus? Thanks for answering. :)