The puzzles are challenging and original, the story fun, and you get many hours of play. I prefer it to the first Unwritten Tales, though that one was quite good.
Initially Critter's gibberish is annoying, but I got used to it and came to find it endearing. And there is a a pattern to his dialogue that provides some clues.
One criticism is the needlessly snarky portrayal of an environmental activist - I can see people being offended by it, and for no reason.