It's a good quality manga, simple as that!
Solid characters, offers great humour, with deep and complex enough plot. When the twists happen, they don't seem repetitive, or forced, or stretched out. Just enough of linger, clues, curiousity, and growing revelation. If you like talking about theories or predictions, or overall a manga that makes you think, this is the one for you.
And of course, the art is quite lovely - well paced and well drawn.
It says a lot too, because prior to reading the series I was already VERY sick and tired of the Alice in Wonderland themes going on everywhere. So it goes to show how intriguing it was to actually lug my arse into trying it.
Fair warning though, read carefully or it can get confusing. No lazy reading, glazing or skipping chapters. It looks like a pretty manga, but it isn't a fluffy or typical one. You might have to get used to some aspects of the storyline overall. Once you do though, it will feel more smooth.
Some of the characters can be a tad cliched (Or can do the odd cliched thing) but the majority are intriguing, unique and likable, with plenty of growth surrounding them.
It is not my all time most favoured series of all time, but it it's a top contender. It keeps me going at least. Highly recommended!