I loved Collections on the Sony Readers, but I have found that the Opus' folder system, combined with calibre metadata to be equally useful. My genre series are all nicely orgnized in folders now, with next to no effort on my part.
There is a nifty post in the Bebook forum on how to set up how Calibre names and exports books on the reader, that builds the folder structure to your specifications. It will involve duplicate copies of the book if you chose more than one folder structure.
Here it is:
https://www.mobileread.com/forums/showthread.php?t=86466