I got addicted to Blitzball at one point.
I didn't think I'd like it very much after I didn't havea clue what was going on in the tournament which I lost the first time, but that was because I hadn't worked out to put the controls on manual yet... it's so much easier now.
And even though it ended up being easy to win every game, I still really enjoyed playing it, even if I didn't need the prizes any more. It just seemed really addictive.