Compared to the first season of Kuroshitsuji, the second season has better plot, if some filler episodes were excluded. I really think some middle episodes (3-7) are not necessary and make the whole story a bit out of track. It'd be better if the staff let the story developed gradually instead of filling the viewers with some irrelevant episodes then rashed right to the peak.
In terms of animation, there's (almost) nothing to complain about.