We watched the first couple of seasons of Six Feet Under, but Michael C. Hall didn't do much for me then. He wasn't hard to look at, but he didn't do much for me, either.
When we saw him on Broadway in Cabaret, he couldn't fill the shoes of Alan Cumming (whom we had previously seen in the show). He did a good job, but it just wasn't the role for him. Again, he was nicely built (too well built for the role of the syphilitic emcee, actually), but he didn't do much for me.
Now he's before me again, and things have changed! We've just begun watching Dexter (on DVD from Netflix), and he looks GOOD! Maybe it's that he has some color to his skin now. Maybe it's the color of his hair (it looks redder than before). Maybe he's just aging well. Whatever the case, he's easy on the eyes!