I watch some singleplayer streams mostly for the entertainment value. Just watching someone play isn't very fun, but some streamers have funny commentary and play the game is weird ways.

It's not very fun watching someone play Fallout, but it's entertaining watching someone play Fallout role-playing as a homicidal maniac that uses nothing but his bare fists. The sheer difficulty is impressive, and if coupled with a talent for presentation/humor it can be a pretty fun time.

This is a good idea for a stream unless someone is already doing it. I remember people doing hard runs of games like that, beating the whole game without any weapons etc. I'd definitely watch that if I'm interested in the game already.

SpoilerWarning does exactly that https://www.youtube.com/user/SpoilerWarningShow/playlists