Seriously, I tend to appreciate visually off-beat movies, Frank Miller wrote some of my favorite comic stories and Robert Rodriguez directed on of my favorite movies, and the cast looks very promising.
Besides, a movie has to have more than a hot actress in skin-tight leather... I never did see Catwoman and by all accounts I'm glad. I could tape a picture of Halle Berry above my cats' litterbox and get the same effect.
But Sin City looks good. Alba in leather is just a bonus :).