After much trial and error, the ONE thing I've tried that actually worked and worked well is ammonia and water.
Remove the front vinyl or paper part of the wallpaper, leaving the backing. No need to score it. Well ventilate the room (this is REALLY important!). I use equal parts ammonia and water in a spray bottle. Fully saturate a section of the wall paper backing and let it sit for a few minutes. Sometimes whole sheets will peel off, sometimes you'll need to use a plastic putty knife to scrape it off but it shouldn't require much of any effort.
Just remember, ventilate, ventilate, ventilate!
Good luck!