One potential option you may wish to consider is the Gnome-Shell Alternate Tab extension
It is the traditional Window-based Alt-Tab switcher that Ubuntu users have grown up with.
- Windows are not grouped by application, nor by workspace
- Thumbnails show window previews
- Windows are sorted by time of focus
It doesnt meet your question "active desktop" criteria - however it does make switching more obvious and easier when you have multiple windows opened.
It is packaged in a PPA
sudo add-apt-repository ppa:ricotz/testing
sudo apt-get update
As with all PPAs - these are testing for testing purposes. Either have a full backup you can restore with or use
ppa-purge to remove the PPA
sudo ppa-purge ppa:ricotz/testing