First the objective stuff:
Audio, visuals, voices, stability, atmosphere, characters all 5/5.
And the more subjective:
Puzzles 4/5. Personally I liked the generally logical/common sense puzzles, but others might find them too easy.
Replayability 1/5. Unfortunately it's completely linear, but I'll probably replay it again sometime for all the 5/5 things. I nearly rated the game 4/5 overall because of this, but adventure games are not generally very replayable.
Overall the game is very charming. It boils down to the usual adventure game fare of pixel-hunt, examine, pick-up, experiment but the characters and environment drew me in to the extent that I generally forgot that I was going through this cycle. There is also a keyboard key that highlights all areas of interaction on the screen, but I hope you don't find it as it can spoil the game.
Would I buy a sequel from gog.com? Yes!