Personally, I absolutely LOVE it. My package also includes the movie channels (HBO, Starz, etc), so On Demand has so much to offer for us. My kids also have a ton to choose from, so they also enjoy it.
Its pretty weak and limited. I do like the option to download the app and have the ability to watch some shows on the go. But the channels and shows are limited. The on demand service is decent when you get the shows you want but they show up a long time after the actual program has aired and they only last for a few days before they change what is on demand.
Its not bad. Some channels and shows are not available and of course if you don't have the channel you can't watch it. I have never paid for any of the shows/movies. They get enough money without that.