I spent a truly obnoxious amount of time importing my music library into beets. It took a couple of weeks to get to 95% imported, and got so bogged down in the last 5% that I never completed the import and never switched over.
This isn't necessarily a fault with beets, really, but a model mismatch. The model of beets is very, very strongly tied to associating each imported item to one well-known, commercial release. While it's possible to stray from that, it takes tons of time and experimentation to cram some things into its model.
Purchased, popular albums are a breeze; they import nicely and make sense. I struggled differing amounts with:
* brand new indie label releases (bandcamp)
* commercial albums variants missing from musicbrainz/discogs
* non-commercial albums (self-released CDRs)
* fan-recorded concerts
* fan-recorded festivals (a special case, a true nightmare)
* fan edits/remixes of commercial releases
* playlists & mix tapes
* mixed media releases
Each was eventually possible, but sometimes it took hours to figure out how to import a specific folder. Worse, after doing one festival it didn't necessarily make it easier to do the next festival. Even if I get to 100% imported, additional imports will still take thought.
This isn't an argument against it, I still think it's a fantastic tool. Just understand that the farther you stray from collecting commercial releases, the more of a struggle it is.