I don't have enough superlatives for it. I'm > 300 hours in between three characters, and I'm still finding new stuff to do. Even at full price, worth every penny. Also an amazing co-op experience - played through the whole campaign with a friend, we both agreed it's probably one of the best games we've ever played, period.
It's also the first game of this genre that I've played, off the back of this I also picked up BG1 & 2, and Neverwinter Nights, which I'm excited to try out to see what I missed out on back in the day.
For digital copies, they could bury this into the EULA and make it a requirement that you agree to it before you make your purchase (IIRC some storefronts do this already).
However for physical copies I suppose there could be a case made if the duration of support was not disclosed at the time of purchase (or it was not printed somewhere on the outside of the packaging).