Of the games I've played a lot/know well:

VII: smurfing Kalm flashback. No, I know it's not an original answer, but it's an hour of the game coming to a screeching halt and just being STUCK. The flashback is boring as smurf. It's the worst, dude.

VIII: Literally all of it. Worst game I've ever played. And I played Shadow of the Colossus.

IX: Love this game though I do, Dali is smurfing dire and it takes way too long. Honestly, really, the first disc up until you leave Lindblum is a huge slog.

X: Luca. JESUS it's just boring, ugly, and forcing you to play Blitzball is a cardinal sin. It's amazing how much better the game gets after Luca. Also the Calm Lands. Basically my exact same criticism for Luca, minus the Blitzball.

XIV: Titan storyline/Company of Heroes. WHAT WERE THEY THINKING?