I'm not much for streaming, and GP seems kind of stream-y, but honestly it's really changed how I play games. It feels like I'm getting demos for games I wouldn't ordinarily try out, and the full game is right there anyway if I like it. And since I don't feel like I own the game, I feel no compulsion to keep it installed. Six of my most recently played games on XBL are from the last four weeks, and far exceed the cost of what I pay per month - I didn't play all of them to completion. I feel like I get my money's worth out of it.
The only ActiBlizz game I have any interest in is WoW. Given what I think of WoW in it’s current state, it would certainly not see me going to Gamepass. All I am playing currently is Elder Scrolls Online.
Depending on how they push WoW through this will depend on whether I stick to it or move completely to FFXIV. Time will tell.