Disclaimer, I'm not actually using Outlook.com myself but I have a dummy account where I checked the following stuff.
1. The "delete" button, next to the navigation arrows is not a delete button. If you hover the button it says "Back to messages" and it does exactly that.
2. The top menu would be quite hard to operate if there weren't any visual cues which button you are hovering, but there are some - You can clearly see at any time which button you are going to click.. The placement of course can be discussed, but looking away while clicking will also not work on GMail.
3. It's argued that Outlook would not respect the "default" use cases. But then, I don't get why it's confusing that your e-mail is classified as junk if you click the "Junk" button. What should happen instead?
4. Reading pane is actually no mistake but used by MS since forever to name the place where your e-mail is previewed.