Missing features:
Any kind of customisable ringtones (even iphones can have ringtones, even if they try to make you pay extra for them)
Outlook sync with PC (again, every other device seems to do this these days)
Full rotation support (they keyboard is ever so slightly bigger in landscape, so why do you have to type most things in portrait mode, such as IE)
Some kind of file system (WP7 feels like we've went back into the 90s with the limited phone interface, its not a PDA anymore!)
backgrounds
a *real* GPS program (no bing maps does not count)
someway of switching between the multitasking programs (yes i know, January update, this still could have made it into the release)
In essence i'm not sure what WP7 has *added* from WM6, sure multiple exchange accounts, but I only need one, sure it's faster (ok i don't have a clever comeback for that, it is a lot faster) but it seems to have removed many many features...
I still love it though, makes me feel happy that it's been out 1 month and is already nearly as gud as an iphone, way to beat them at their own game!