Give the developers (including me) some time to ingest all this. It ain't simple.
I'm more or less saying that knowing a lot of the metro design concept and have used software designed with such for a couple of years now, I think I could render some services helping developers to make a beautifully designed Windows 8 app.
I would say that Xbox Music is nicely designed, but it's not. Honestly, the Zune software's UI could had been used for some it. For example, the music library (or collection) screen filtered by artists would had been perfect; you can scroll through on the left side through your artists, scroll through albums by artist in the center, and scroll through songs by artist on the right side. And it would had been better to put in better filtering. The main panorama screen can be kept in Xbox Music, but making it a little more....metro. Some of the UI controls can be taken down a notch as it isn't too difficult to tap or click on them. A better Now Playing visualizer should be used, like Zune's. There just isn't enough of the digital motion, or animation, to Xbox Music like there is with Zune. They're usually subtle and here and there, but it makes the user experience better, at least to me. Xbox Music doesn't offer that. At least YET.
OH! I just remembered, the Tom's Hardware and Guide apps. They're nice, but not totally giving the feeling of immersion. I'd like to see some more full fleshed content mostly. A good way to organize would to break up the different subcategories into a main panorama, where the most recent content is show. Kind of like the way USA Today does it, but different, it would show more per section. I wonder how it would look like too if the different sections of the panorama had photo backgrounds. For example, the Reviews section would have an image from each review article, like an AMD Radeon 7870 review would have that as a relevant image, and those different images would be in a mosaic. The best example I can give is on The Verge's website, where they have the day's top articles and posts in a colored hue mosaic.
If I were to design an app in general, I'd use system accent colors, kind of like how Windows Phone does it. Windows Phone apps that use the system accent color give the overall feeling of everything being integrated. Third party apps feel like native first party ones and such. Windows 8 needs to have some of that I believe.
Actually, the way the screen designs are done using XAML this is exactly the design mode that Microsoft is trying to encourage. They have Visual Studio for prototyping and developing the app itself and the "Blend" application for graphic-designers to design the actual appearance of the GUI. The programmers themselves don't necessarily have to be in on the front-end design other than the basic functionality of the app. The graphics designer would then take the app and "pretty it up" using Blend.
I wonder if it's easy to learn(probably not) the coding for the apps. The biggest disappointment of the apps comes with xbox music and video, zune software was great(especially a few previous versions) zune HD showed good use of typography and visual cues. Xbox music/video however is a bland and depressing. Gradient grey in the background looks like a prison. The only good thing is the tracking button on the trackbar while in the newest iteration of zune software it's hard to see here it's much easier even though the color is not ideal. Other than that though it doesn't have the fun of the zune software it is replacing(assuming it is supposed to be a replacement). Assuming they are following design principles there is some functionality that needs to be worked on.
That's not to discourage you from trying it, just be aware that it's like any other discipline. I've been doing it for 36+ years myself.
There was once a picture I saw of that describes how a novice game developer thought it would be like, but really what it's like... I wonder if I can find it...
What bugs me most about this Aero thing is that there's no technical reason why it had to be removed. If you point at the lower right corner, the Aero Peak function still works and even has different levels of opacity for layered up windows. Even if you pull up the Charms bar and look at the clock it has some subtle transparency to it. I can do without the glass stripes, but I liked the transparency. The blur would be a huge bonus but I'm alright without it.