This is not a new version of the existing Eclipse (or Intellij). It's not a desktop app at all, it's a web server that starts and then your browser opens the EclipseCHE "web app." The IDE is merely a web interface - everything is happening on the CHE server (which would make the most sense if you install it on a separate machine altogether).
As far as the IDE, it's actually kinda amazing for a web app. If the browser chrome was missing it would seem like a desktop app (except the menus are in the wrong place for OSX). The intellisense doesn't seem to be working yet as far as I can tell. Maybe this is just PHP, though? It shows valid PHP code highlighted in red as if it were an error (edit - restart seems to have fixed this). I wish so badly that one of the dark themes for Eclipse looked this good, though. I've tried for days to get a decent dark Eclipse theme going - they all suck.
It seems that it may be creating a docker container for your project. You don't open local files on your machine (there is actually an 'upload' function to add a file to your project though). The files don't exist on your normal filesystem - they exist on the server, perhaps in a container, or just some internal folder structure that the server controls..? It seems to want to handle it all magically, which means I can't easily try it out on one of my existing apps. This is not really normal for my PHP workflow, but perhaps it would be perfect for those who have their app already in docker containers?
I can't get an application to run at this point. I have docker installed, but it just hangs with the message "Your request is queued waiting for a node to become available..."
Overall, it looks extremely interesting - especially for a team environment where everything is containerized. Just point a new team member at a URL - and the IDE and server environment is 100% set up, ready for them to start coding, debugging and running the app. There would be essentially zero setup time for working on your app.