See it twice.

Rating: 9/10 (12 March 2010)

And the second time you see it, don't see it in 3D. It's more enjoyable and less "visibly dark" in 2D. First of all I don't think the reviewers are giving enough credit to how amazing the visuals are. Virtually the entire film was green screened and it never feels like that. You as an audience member believe they are in this world and these creatures are next to them interacting.
Also, seeing it the second time around you get much more of a sense of the theme, especially with the parallel of when Alice runs from her proposal and later when Alice runs from being appointed "the champion".
And really the people who compare it to Narnia and Lord of the Rings are overlooking the fact that though basic structures of the story seem similar, there are elements such as Alice's growing and shrinking throughout, and the bizarre animals, and the Queen's humongous head that really live in that world of Wonderland (or Underland rather) and couldn't adapt to a Narnia or a Tolkien book.
Acting wise it's all fine. As many other reviews have said, Helena Bonham Carter steals the show, and I think to a certain extent Stephen Fry as the Cheshire Cat does too. Mia Wasikowska's take on Alice I found excellent. She's not bland, but makes subtle acting choices and I find it much more powerful. Linda Woolverton's script however depicting Alice as certain she's in a dream for more than half the movie makes Alice come off a bit like she's less engaged and in awe of the world around her. A flaw that lies solely in the script.
Overall thoroughly enjoyable, imaginative, and a fresh new take on such a familiar classic.