Really cool.
I suppose I should start off with the parts of this I didn't particularly care for, just to get it out of the way:
There were a few confusing parts to this, and I saw a lot of places where more description would be nice (for example, what was that fire-looking thing? who was speaking to him? what were the monocle'd man's motives? etc. etc.). I know it's harder to do that in a video with very little dialogue, but it's not impossible. The art is rather simplistic and could use some work-- in more serious stories, I like a little more detail. But maybe that's just me...
Now for the parts I liked.
Despite a couple plot holes and moments of confusion, this was really good. I know from that bit up there that I wrote, it may seem like I didn't like this, but I assure you that I was just being critical; this is actually really good. The concept is great, and the design of the guardians was pretty awesome. The music was beautiful and gave the story a bit of a wild, ethereal feel, and you synced it with some of the scenes pretty nicely. It was involving and interesting and it would make a great series. I don't know if you've done other stuff with these characters or this universe, but I really, really hope you develop this story. You could do some really great things with this.
So yeah, it was good. :)