I finally got around to composing some thoughts on what I think about Windows Phone 7, and I posted those impressions on my personal blog. I'll save a few bytes and not repost it here.
It should be obvious that my general impression is overwhelmingly positive. What I don't go into very deeply is how much I enjoy developing stuff for it. Baby Stopwatch was not even remotely hard to build, because it wasn't complex, but also because the platform itself is so easy to deal with. I've been messing around and building something a little more involved, and it too has been fun to work with. Sure, you have the quirks of Silverlight to work out, and then the phone-specific quirks after that, but it really is a lot of fun. If you haven't come up with a science project for the phone, I would encourage you to do so.
Now if only I could find a gig here at Microsoft where people just build phone apps all day! (But not games... I know we already do that quite a bit.)