Beautiful.
I understand you were going for somewhat -- an artist game, I certainly can't disagree with that, it looks great, plays great, it's all very pretty. But besides that, it has one small downfall, it's gameplay.
To set the story: you're playing a fox (Sly), as the story continues we're told you usually go hunting for mushrooms, however your master (William) asks if you can activate the runestones that are in the forest. So there's your main objective, watching out for darklings that will likely ambush you on the way.
Sounds easy enough, but if you want to rack up some extra points at the end you can do the optional objectives, slaying darklings, gathering mushrooms, switching leavers, etc.
The controls are fluid and they work perfectly. Graphics are without a doubt the best in a flash game I've seen for a while. Sound choice was perfect, it suited the artist feel of the game, this creates a great atmosphere.
As I said previously, the gameplay does let the game down slightly. It's tedious, a little boring in fact. I think that will only apply to others who are getting the achievements though. You can easily just get your main objective done and finish. The game is huge, and it does feel longer than it should. That's what generally let this game down, it's just short from a 10/10.
Overall, a wonderful game. If you enjoy the classic -- run around, get this, that and that too, you'll love the game in everyway. So I'll leave William and Sly with a 9/10.