Disclaimer: I haven't finished yet, I'm probably around 8 hours in.
This game is wonderful, it's fully and well voiced, it has a beautiful art direction (obviously for such a concept), it has really nice characters with pretty deep narratives (K&K and surroundings was such a fresh approach to conflict within video game narrative design for instance), it throws me back to some Oblivion feels (which is one of my favourite games ever), it's actually full of content (I didn't expect as much), and it has a nice and subtle sense of humour.
It has literally one downside (and I decided not to take it into account in my rating): performance and stability are pretty terrible. I think I counted something like a dozen crashes in a day's worth of playing (at least it autosaves on every conversation, otherwise I'd have cried a lot). As for performance, I keep getting hitches and low framerates on decent hardware, and my friends who've played the game report the same problems.
EDIT: I've finished the game and I have to reiterate, this game is brilliant. After some updates by the devs, the game isn't as buggy and poor performing as it used to be. I simply cannot wait to see more, I'm hooked :)