I am not terribly impressed. The ability to build and run apps in a well defined and portable sandbox environment is nice. But everything else is kind of terrible. Seemingly simple things like having a package that contains multiple binaries aren't properly supported. There are no LTS runtimes, so you'll have to update your packages every couple of months anyway or users will get scary errors due to obsolete runtimes. No way to run a flatpak without installing. Terrible DNS based naming scheme. Dependency resolving requires too much manual intervention. Too much magic behind the scene that makes it hard to tell what is going on (e.g. ostree). No support for dependency other than the three available runtimes and thus terrible granularity (e.g. can't have a Qt app without pulling in all KDE stuff).

Basically it feels like one step forward (portable packages) and three steps back (losing everything else you learned to love about package managers). It feels like it was build to solve the problems of packaging proprietary apps while contributing little to the Free Software world.

I am sticking with Nix, which feels way closer to what I expect from a Free Software package manager (e.g. it can do nix run github:user/project?ref=v0.1.0).