Funay!
It is indeed very good... But let's get right down to it... It has at least one annoying flaw. You have to be very careful if you want to place a domino in a tight spot, because when you release your mouse-button you might just knock over a domino, and then it'll start from there of course. That's probably the main downside of the game...
Also, the physics of the dominos can be argueable. Sometimes you think that by eyemeasurement that a set of pieces are alligned correctly, and then one of the dominos doesn't tip over the next domino. Frustrating, but I guess it comes with practice.
Other than those "issues", which every player can get adjusted to, it's a really fun game. Of course it's just dominos, but for those lazy bastards out there, who can't be bothered with doing the hard work, alligning the pieces 'n all, they can do it here. And if you give it some effort, you can actually get some pleasing results :P
Worth mentioning is that the game runs pretty fluintly, even with all the animation and stuff that's going on in the scene. I don't know it this is anything spectatular, but often when you have a game, with a lot of animated objects in the same scene, it tend to lag... Or sumfin'...
It may be a very simple little game, but actually I can't find any reason to give it less than a nine overall. It may not have a lot of variety or a wide gameplay-aspect, but it's fun and kind of original.
Well, yada yada, good job. Sorry for my lacking in the english language. But to my excuse it's early over here.