Tried installing Retromania ....this thing took over Kodi with a new interface...can't even navigate to systems, etc. My screen now has "Anonymous Test Zone'
Does the UI look similar to the video? Is it usable? You can do a fresh start under the settings or system tab in retromania and your kodi is back to original look you're used to. I did a fresh install and for me the retromedia worked when installed new on a fresh kodi version on MINIX system. I can give you the guys e-mail or you can join the Facebook group for any help. They are really good and one of the devs is from Mississauga.
This is a total package so it will change your UI, however you should still be able to add other add-on and you can even change the skins.
Just PM me and I'll send you his e-mail if needed. If not, just delete the kodi app and reinstall it and do it on a fresh version, then it should work. I think they updated the UI and will look a bit different from the video in this thread but from the Facebook comments it seems to work good. I also had no issues with the previous version with the Christmas theme. It takes a bit of time to understand what you're doing if this is new to you, but once you understand it really amazing the functionally it brings, all the free movies, sports, TV shows, live TV, games etc....
This is the intention of a package like The Beast, or The Spartan, or Retromedia. It installs all these packages and sections onto your kodi with its own skin. You should still be able to do the normal kodi functions, however it takes a bit of understanding. Nothing to worry about.
As practice do it on your phone if you have an Android phone. Install the kodi app from the Play store, follow the instructions in the video, and be patient. It will be worth it once you understand it and give it a chance.