I'm sorry to have to chime in with the negative here. I do have some appreciation of sleek design, and I have yet to make a final call on iOS 7, but this is not working on iCloud. There are areas that are better and worse, but things that turn me right off:
* The login screen actually looks like something Microsoft would do. Nothing wrong with that, they've done some decent designs, but the identity of it now feels Windows instead of Apple. Doesn't mean it should stay the same as it was, but now it looks like 'that other company'.
* The Mail icon looks like something I'd draw with CorelDraw back in the 90s. The gradient is horrible and the whole thing looks cheap. I don't think the old iCloud icons were brilliant as they were, but this is awful.
* The look and feel of Mail is dull and uninspired, and uninviting. Blue and grey with spidery thin vector icons. Again, has a very 90s aesthetic to it. Like using X11 on a UNIX box before colour and actual graphic designers were introduced. The folder icons simply look like some rather shoddy opensource hacker icons. No attention to detail, no proportions. Bad, bad, bad.
* Similar vibe with Contacts. It's all very 'techie' and not particularly beautiful.
* Calendar looks very corporate. No balls or fun. Kind of like the apps Google puts out. Actually 'corporate' would be the description for a lot of the other things too. Now I totally *loathed* the stupid turning page animation in Calendar on OS X (not so bad in the iPad, as it sort of fitted with turning pages with a finger), but this other extreme is not doing it for me either.
* Notes: boring. Grey. Corpoate.
* Reminders is actually better. The colouring and contrast gives it at least some life. Not fantastically inspiring, but not an immediate turnoff.
* Find My iPhone is OK.
* On the plus: the icons for Find My iPhone and Contacts have a nice minimalist vibe. Colours, shades and proportions work. Calendar is also OK. But ugh, that Mail icon needs to go. Switching from one 'app' to another is nicer.
Updated to add: I'm also concerned about so much focus on reinventing the design, versus improving usability. Many would talk about 'Apple eye-candy', not realising that their design was never just painted on. It was always about making the experience more joyful, easier, faster. Others tried to copy that by merely painting nice colours, but would always miss the point. Now there seems to be a real lack of innovation in actual usability. Designs always need to be refined and updated, but hopefully not at the expense of what really matters.