Analysis: The visual presentation of O Quarto was what originally drew me to the game. It has a very quiet, interactive painting feel to it. The visual cues and sound it plays when you discover an item is strangely rewarding. O Quarto also has a good sense of humor, though be warned that there are a few instances of words not quite safe for children.
As far as the puzzles go, O Quarto doesn't go to the extreme and hide things in completely undiscoverable places. Yes, you do have to do a bit of clicking, but for the most part you'll be able to find items fairly easily. Not too difficult but challenging enough to make it just right. When I first discovered the game I brought the link into our IRC chatroom for help. Thanks to the heroic efforts of Valarauka and Harukio, we managed to complete the game without any loss of sanity and/or limbs.
Great visual style, good puzzles and the possibility of a sequel, O Quarto is a worthy room escape game to spend your time on.
Looking for a walkthrough? Cheers to Wolfgang for posting the... O Quarto walkthrough.