Being an avid fan of Kuroshitsuji, and seeing the entire first season, OVA as well as being an avid manga fan, I must say that I'm disappointed in this series for several reasons. This is merely an opinion, but I found myself hating the storyline behind season 2 entirely.
Below are the good, bad and ugly of this series:
The series has amazing artowrk and beautiful sound.The animation was crisp and clear and the music was amazing, especially with songs coming from Yuya Matsushima and Nightmare.
The bad, and the ugly.
As several reviewers stated before, it does not follow the manga, but I don't consider that bad because a lot of anime follow this trend. The storyline had actually stopped following the original manga plot during the Drocell arc in season one.
Also, this series started off with a filler episode as the second episode. That is a big no-no for any anime. You start off the series by building up the plot, not doing a filler episode that, regardless of whether you watched it or not would still understand the story.
Out of character moments. There are several large out of character moments and things that were brought up and dropped. In one of the episodes, Viscount Druitt (who has a medical degree and offered to sell off the protagonist, Ciel Phantomhive in pieces on a black market auction) fainted at the sight of blood. It was rather vague on if he was extremely happy in seeing it, since he had sadistic reactions to the previous battle, or if it was because he was woozy but I found it very out of character. There are several other moments in Ciel, Sebastian and a few other characters that I found out of character.
Unexplained changes to characters. Several relationships and things about the characters were not explained or elaborated on, which made a very obscure plot and caused general confusion among fans who had been following the series faithfully.
Fan service. To be honest, in my opinion, and don't kill me on this, but this series was written like bad fanfiction and left many answered questions. There was also a huge amount of fanservice and hardly any of it was presented in a way that I thought was well thought out or tasteful in the slightest. The setting and time period for this show went from elegant to trashy and it caused the series to lose it's appeal.
There were also too many of what I call 'scenes of convenience'. Several characters had the opportunity to be interesting and have a good amount of spotlight but were disposed of in poorly executed ways. Viscount fainting was a poor excuse to get rid of his character during an important scene where he could have taken active role in the plot. He was actually promised a very good storyline with watching over Alois but it was disregarded shortly after wards, which was a let down to me, as a personal fan of the characters. Also, as good as the first episode was, shoving Ciel and Sebastian in it all too quickly, as if the say 'Look! They're still in this season!' Because the writers were afraid of fans not being interested was a poor decision in execution as well.
The show had overall poor execution and a lot of things were unexplained or left off. The episodes got more and more ridiculous after a moment in time and I couldn't find myself watching it after a while. It became a chore and not an enjoyment. As a Kuroshitsuji fan, I'm sorely disappointed in this season. As an anime fan whose critiqued anime for 4 years, this is the worst I've seen in a long time.
It's nothing but a case of bad fanfiction turned into an animated series. I expected a lot more from Kuroshitsuji. It only got worse as the series ended. If they make a season 3, I might not even give it the time of day. There are better anime out there, I implore anyone who reads this to stick to season one, or they might end up just getting angry.