Blitzball was total shite, cant defend it, just terrible.... (FFX-2 version)
(meanwhile FFX)
Now that i have that out of my hair, i have to say that it was an enjoyable time sink. It actually had decent mechanics with the players, and the gameplay wasn't too bad (minus the chase the ball AI). however if they had more animations (try shooting it pass 3 people and the goalie...) and didn't have a major exploit (hide behind your goalie ftw) it would've been beyond awesome. Add into the fact that you can get a couple of cool moves, and unlock Wakka's ultimate weapon with it and it becomes an epic game.
Really if they had a 3D version instead of moving on a single plane, it would've been worth a standalone game to me.
However if we talk about FF minigames, i have to go with FF8's card game as well. Quick, fun and takes forever to get all of the cards. (never wanted to get rid of ifrit, originally i thought i couldn't get it back)