I'm using Banshee 2.2.1 on Ubuntu 11.10. When I tried to import my music library, which I made by ripping CDs with Windows Media Player, only two albums retained their information. The rest (about 300 songs) were dumped into the unknown artist, unknown album folder. All of them have names and some have genre information. The two albums mentioned retained everything: artist, album, names, art, etc. I am not completely sure with what I ripped these albums.
If you select the Unknown Album of the Unknown Artist, Banshee will display the corresponding track-list (which should contain all the unidentified tracks you imported).
Select all the unknown tracks which you believe belong to a same album (using shift+left-click or ctrl+left-click), then right-click to get the context-menu. In this menu you will choose Edit Track Information:
You will then see an Edit Track Information dialogue, where you will be able to edit your metadata manually:
There are also plug-ins to fix metadata.