First up, Martin Freeman as Bilbo. Costume design is nicely in keeping with the stuff Bilbo wore in the LotR films, but different enough that it's believable that a (comparatively) young character would wear it. Hell, Freeman even looks like a young Ian Holm. Very good choice for the character; so far, Bilbo's looking good.
The dwarves... I'm more hesitant about. They still look good, and it's nice that they appear to have decided to make each dwarf look very distinct; given how many of them there are, this will definitely be handy when it comes to keeping track of who's who. Now, I know The Hobbit is considerably more light-hearted than LotR, but I worry somewhat that the designs are a little, well, silly. Still, this is mostly just nit-picking. I'm still stupidly excited for this film.
Ok, fine. The dwarf on the left has hair that wouldn't look out of place in a Final Fantasy game. But other than that it looks good.
All pictures come from Empire Online.