In the end, it's hard to review a series that's an anime-original sequel to a series that had an anime-original ending. The source material's relevance in all this is somewhat muddled - neither series really reflects a continuity with the manga. That said, the truth is that, for most of its two-cour run, the first series was mostly faithful and derived from the source material. And the second was almost completely new material. And that led to some very distinct and important differences.
A lot of how one feels about this sequel comes down to how they liked Alois and Claude, as well as the new supporting characters. For me, that pairing was never nearly as interesting as Ciel and Sebastian. Alois did become more of a layered character as his backstory was revealed, but he was an unpleasant lad - vulgar and cruel and frivolous, where Ciel - for all his misfortune - always carried himself with a stern dignity and grace. As for Claude, he never impressed me as anything much more than a pale impersonation of Sebby. Hannah probably turned out to be the most interesting of the new characters - complex and surprising, and ultimately the instigator of all the major events in the story.
There were certainly some identity issues with the series as whole. Some of that schizophrenic tone was intentional, I think, but still - a lot of time was wasted with mediocre episodes in the first half. Those eps felt like a fairly good rip-off of Kuroshitsjui rather than Kuroshitsuji itself - the elements were there, but something just wasn't quite right. But fortunately, that turned around in the second half as the story focused where it needed to and it became clear that each pair had a vital role to play. Of course the fact that we only had one cour this time was important for a number of reasons, and that fact also makes the wasting of so much time in the early eps that much more galling. But it also caused the series to be much more frenetic and action-driven that the first one was. This was a major difference in tone for me. The first series had a real sense of gothic horror to it - leisurely, darkly funny and quietly disturbing. Everything was bigger, louder and faster in the sequel - the humor campy, the conflicts more obvious than implied.
In the final analysis though, I think this show ended up being better than I expected after the first few episodes. It did manage to capture something of the true feel of the material, if less so than the first one. Considering that the material was 100% anime-original the plot held together pretty well - it progressed logically, secrets were revealed at an agreeable rate and the resolution felt somewhat true to the story. But as I said in the episode review for the finale, I think that one's overall view of the series will largely depend on how they feel about the ending.
Have a nice eternity, Ciel and Sebastian. See you in Wonderland...