I'm sorry but 10 and 9, particularly 10, were way better than 13. I didn't mind 13, it was an alright RPG, but its a shadow of what Squaresoft used to produce. 13 had detestable characters, a main protagonist with no personality or anything interesting to say, a villain who didn't show himself until 30 hours into the game (and whos motivations and final goal still make little sense to me) and a plot that plodded along and yeilded nothing particularly interesting. What XIII did have was a great battle system, wonderful graphics and (once it finally opened up) some rather decent quests and 'boss fights'. But that's exactly what was wrong with it, Final Fantasy is a favourite amongst JRPG fans for its storyline development and characters as much as it is about the gameplay (perhaps even more-so with the best titles, FFVII for example offered nothing particularly ground breaking or exciting in terms of gameplay, the storyline is what drove me forward and created excitement). Even the ending was naff, they spend their whole time saying they want to prevent cocoon from getting destroyed, then go and destroy it (and, other than fang and vanille, none of the main characters knew that it was possible to save the inhabitants after killing orphan, so why would they happily join in in killing what they believe is what they were meant to defend?)
IIRC X-2 was the first title that had the SquareEnix logo at the start, i too believe there is a notable decline in the quality of the series after SquareEnix began its lifetime. I'm still waiting for what i'd consider a 'good' Final Fantasy game, 12 was okish, but none of the other titles have even competed with X and below.