Well, it's much better than New Moon, but that's not really saying much. Among the list of improvements are a reduction in the number of so-cheesy-it's-funny moments, the humour actually managing to hit the mark a few times, and the story at least making a bit of sense. The real improvement of this production, though, is the action and the cinematography; both benefit greatly from David Slade's direction, and this alone makes this movie watchable. However, the action is so improved (which basically means that it has evolved to simply being lacklustre compared to proper action films) that everything else now seems even more dull and uninspired than usual. All but a few scenes involving Bella, Edward and Jacob fall flat, which isn't helped by the poor subject matter and the awful acting. The viewer basically finds himself impatient for the end of the emotional scenes so he can get to the wolves biting off chunks of young vampires.
Actually, even the action scenes are sort of anticlimactic. The whole movie builds up to this epic, deadly, nearly hopeless duel with an army of savage and semi-legendary vampires, which actually ends up being only a few minutes of everybody easily slaying all the evil vampires with only one person sustaining one minor and inconsequential injury. Pretty lame, though still probably the high point of the "saga" so far.
Basically, it's better than New Moon, inferior to the "pretty good" original, and you'd forget about it fairly quickly if it wasn't so overhyped.
In a sentence:
Better, but lacklustre, action makes everything else seem even more boring than usual. Still, the humour works sometimes and the story makes more sense, so it's an improvement.