Well can basically say I haven't paid for GamePass, as I just paid for 3 years of Xbox Gold Live (3 x R650) ... and got GamePass Ultimate for free.
In the 5 Months I had "Xbox Live", I got about 5 games free as in to keep and about 15 others that is "free to play" as long as I am subbed.
Games I finished on GamePass Console: Ori, Control, Medium, Jedi Fallen Order, Squadrons, Dirt 5 and Burnout Paradise
Games Installed but still need to get to: Skyrim, Shadow of Mordor ,Torchlight 3, Darksiders Genesis and Froza Horizon
Games I still need to get to: Outriders, Outer worlds, Gears of War entire series.... Frankly there is to many to list.
Games I finished GamePass For PC: Prey, Entire Halo Series. Busy with Wolfenstein Youngblood's.
What I haven't even touched is the games my Wife plays on Xbox set as home console, like Zuma, Tetris, For the Kings and who knows what else.
Have I bought games on top of that? Hell yes but that is cause of GamePass/Live discounts. I have yet to pay full price for a game.
The real question is actually, when the 3 years passed and I actually need to start paying for GamePass Ultimate or GamePass PC or GamePass Xbox, will I?
Answer: If quality and quantity is the same as now then the R150 p/m is a no brainer. If quality goes down then no, but that is the beauty I can always cancel the moment the value is not there anymore.