If you didn't like Sin City or 300 because of their "style" then you won't like the Spirit. Personally, I thought Sin City was just boring, and 300 was ok but didn't live up to what I expected it to be. I was forced to see the Spirit even though I originally wasn't interested because I thought it looked corny as hell, but it was Christmas and "family time" so I went, and I actually enjoyed it. It didn't feel like a waste of time when it was over, and I didn't pay for my ticket so, not bad. I thought it was a lot better than Sin City/300 but my sisters felt the opposite.
Now if you're a fan of the comic, don't bother, because Frank Miller absolutely butchered the original concept and storyline. In fact, the only thing the movie seemed to share with the comic strip was the title. If Will Eisner hadn't died before they started filming I honestly don't think he would've approved of the movie. I'd never even heard of the comic before now, so that didn't put me off at all, but after looking it up I can tell you if they'd changed the character's names, it would've pretty much been an original piece and nobody would've been able to tie it to Eisner's comic. That's probably what they should've done, because it seems like an injustice to have made the movie so radically different from the original story just a few years after the guy's death when Miller was free to do whatever the hell he pleased with it.