I'm so glad I backed-up all my HD DVD movies several years ago (using a LG GGC-H20L ROM drive) because just about all of the disc's have delaminated/rotted and don't play at all now...
A few of my discs have rotted. Some did not matter too much as I had bought them mainly because they were bargains. Others, e.g. Blade Runner The Final Cut, did and I had to rebuy them on BluRay.
There are a few left that I am sad that I can no longer play.