The protocol itself is designed to be really flexible in the kind of data you can send through it (and therefore automatically propagated to and synchronized with other servers) so it can support a lot of different use cases. This includes standard chat app things like audio/video calls but it could also be used for stuff like forums or even serve as a backend for syncing information between organization (I'm thinking of things like medical information between health institutions).
All in all, there's a lot of potential in Matrix.
The conferencing servers are currently in London however, so you may suffer from transatlantic traffic problems if you are elsewhere in the world.
As an example of what could be improved, I do still encounter the occasional bug with call synchronization, the video stream of one of the sides not getting started on occasion and screensharing is hardly discoverable.
GNOME and KDE are also using Matrix.