I loved Sin City, but after watching Serenity (a film I only went along to see because Jonathon Ross gave it the thumbs up on Film 2005 and I had some time to kill), I bought the TV series, went to see it again (the first film I've done that to since Star Wars Ep4), bought the shooting script book and had the Region 1 DVD couriered over. I guess that makes me a fan!
Honourable mentions for Harry Potter and Wallace & Gromit, both enormously enjoyable.
I probably would have liked Batman Begins if the combination of a late night screening and too much beer hadn't got to me! The first 20 minutes looked good though!