I think it looks interesting. I like the little details like how the screen rotates in an animated fashion, and the overall smoothness of it. I also like the Xbox integration which will guarantee some nice games. Other parts of it seem to lack eye candy. The software keyboards look hideous, and the whole tile thing makes the OS ugly at first glance. I'd much rather look at my homescreen of my Evo than a bunch of plain looking tiles.
But MS is on the right track, and I will definitely be keeping an eye on how things pan out. Looking forward to some full reviews of the new phones when they launch next month.