After some time of using the new Edge I got new insights. First of all, it is not possible to set that closing the last tab in the window does not close the whole browser; e.g. in Firefox in about:config it is possible to set that disabling the last tab does not close the browser. This is missing in the Edge.
Secondly, the personalization of quick dialing on the new tab. Quite a nice solution is to display images from Bing, but the option known from Opera, where the user can choose his own background, would be useful.
You can add your own page links in New Tab Quick Dial buttons now. What I miss is the ability to change default search engine in New Tab search field (not address bar).
Another feature I seriously miss is Google Native Client (NACL) support. Edge Insider comes without NACL included, and it diminishes advantage of Edge compare to other Chromium based browsers, including Google Chrome. The reason is, there are quite a few popular extensions in Chrome Store installed as NACL modules running in a new browser window. MS Edge can attract more testers to speed up the development if NACL is included in Edge Insider builds.