I sort of disagree. The UI is clean but things aren't where you expect them to be and it makes it confusing. For instance, I didn't know where to put the subject when I was sending my first email -- it's huge but it's weirdly placed and unintuitive. I also couldn't find the Send button at first because it's on the Nav bar -- not where I expected.
I also agree with the post below re: branding. I went to "Help" to see what they had and it took me to a windows.com page saying "This page doesn't exist" followed by "Hotmail Help". Nice.