Horrible, horrible, horrible (and no, not just because of the bugs).
Only thing I remotely like is the Win 7 integration which it all finally seems to be working right.
This social stream feature is ridiculous. If it's not set to Friends it looks downright ugly, though as Chris says it may work better once Facebook etc is included. I don't like the new emoticons much, the
emoticon just looks.... umm... homosexual? I don't know how else to put it.
I don't like the personal message being "rebranded" as a Facebook status update-like feature. Plenty of people I know don't use it that way (they more use it as a continuation of the display name) so I think it will take some adjusting to.
It's no great improvement to WLM 2009 I reckon. If they want Windows Live Messenger to become a "social networking hub" then they need to implement different steps. The social stream has the potential to work but the split screen contact list alongside the stream does not work well, the text is bulky and large, doesn't work well without images.
A better step could be to have tabs down the side to switch between contact list, social stream and (why not) your Hotmail inbox. If Microsoft wants us to use the personal message as a "status update feature" then I think it would be better to leave the display name along the top instead of shifted down the page, so at least the casual user can tell it's still the personal message feature, just looks different.
Really makes me miss WLM 8.5 at this stage.