I don't mind the start page, but I hope that we'll have the ability to put Outlook's full "adgenda view" on there and show more than one upcoming appointment. That's one feature I like a lot about the current WinMo platform. I like being able to take a quick glance at the
entire day without fully going into the calendar, like the existing 6.x home screen.
The fact that apps can only be installed via marketplace doesn't bother me either. One of the advantages I see out of this is that we'll be able to update apps much easier. It may also force some developers to "get with the times" and release some updated software.
But I wonder if other small but extremely useful features will make it in WP7, like email/text auto-correct, auto-suggestions and VoiceCommand. PLEASE include VoiceCommand Microsoft! But how would VC work? There's only 3 buttons! On my TP2 I could invoke VoiceCommand by holding the left Phone button, but the dedicated phone buttons will be gone as well.
I'm bothered by the mandated 3 button rule Microsoft is forcing manufacturers to follow. At least give device makers the option to include more hardware buttons for quicker access to specific apps/features like making phone calls without having to press the Home button and then on the phone app.
Microsoft should hire me to do UI testing/discovery LOL. If an OS passes my standards we'll have a serious winner

WP7 will loose major points if the other features haven't or won't be considered by MS.