IMHO it's the best FOSS photo application out there. It's cross platform, fast, stable and manages the whole photo workflow (RAW developing, photo management, non destructive editing). Thanks darktable folks!
At the moment I don't have a good library app, I just browse the directory structure. I've tried Lightroom but it too struggles with my library folder, although unlike Darktable, it is marginally usable. I've tried Digikam, and while it's the only one that seems to handle the library in a semi-respectable fashion (with the experimental, now-deprecated MySQL backend enabled, which iirc took some manual massaging to even make compile anymore), it's hard to get the components I really wanted to work reliably (it's very important the my camera's GPS tags can be mapped and sorted; this is my main interest in a library manager and as of now, all such programs are too overloaded to do this competently or half-broken like Digikam's integration, and when I need GPS-based information I guess I will have to try to write a script that reads the coords out manually with exiftool instead of trying out Yet Another Library Manager).
Adobe is absolutely that 1k lb gorilla in the room that everyone is afraid to compete with. Add to that that photography programs are very difficult and complex work and it makes the field, particularly the field of volunteer developers who make contributions to a FOSS project, pretty limited.
For the record, the current size of my library:
[me@my_host photos]$ find . -name .snapshots -prune -o -iname "*.CR2" -print | wc -l | xargs printf "%'d\n"
97,596
[me@my_host photos]$ find . -name .snapshots -prune -o -iname "*.JPG" -print | wc -l | xargs printf "%'d\n"
177,785
[me@my_host photos]$ du -sh --exclude=./.snapshots
2.8T .
Open to any tips others may have.