OpenHAB suffers from the developers reinventing the wheel every 2 years. I started using version 1 for automating my house in 2015. I didn't bother with the UI, since I'm running a web based dashboard I wrote myself, but the underlying "hub" and plugin infrastructure combined with the REST services and the HTTP eventstream API let me combine my custom scripts and devices (which speak MQTT) with stuff from hardware vendors and cloud services (zwave, zigbee, netamto devices, ebus heating control, caldav). In V1, all configuration could be done via plain text files, and automatically applied when the files were changed. That made it very easy to change the setup while still having it in version control.
Then came Version 2, invented a completely new way of handling plugins and deprecated all the old plugins. Some things now could only be configured via a new UI called Paper UI, which broke my git based config. Luckily, the V1 plugins mostly still worked (though some, including zwave and MQTT, were conflicting with the V2 versions so I couldn't even soft-update the items).
A few years later, they introduced V3 which finally broke the old plugins and deprecated Paper UI. I cannot say much about this version cause I'm stuck with V2 forever - there are some plugins I use that have never been adapted for V2/3.
I hope that I can keep this system running until something better based on the new Matter standard emerges. I played with Home Assistant, but it's not really fitting my use case. I don't want shiny UI, I want a reliable system that connects all my stuff and logs all the changes to a time series database. Bonus points for giving me Alexa AND Homekit support without being dependent on someone's cloud service (besides AWS of course) - which still works great with OpenHAB for me.