I have both Series X and PS5 and the Series X gets the vast majority of playtime due to Gamepass. Pun aside, it is a game changer. What's particularly encouraging is MS are just geting into their stride with Gamepass and it's only going to get better.
There's 3 main benefits. First - all my online gaming buddies having access to the same library of games - so no more trying to convince each other to buy the game x. We all have it already. Second - which ties into the first and most significant, is the freedom to try out anything you like. 4 of the 5 games i've enjoyed the most since the launch of the new consoles were titles on Gamepass that I wouldn't have tried otherwise. Streets of Rage 4, Wasteland 3, State of Decay 2 and Hotshot Racing. Third - it's super cheap. One PS5 game cost me almost as much as Gamepass for 3 years. Even if you don't go the Live upgrade route, it's super cheap for what you get. I haven't had to buy a single game on Series X since launch.
ymmv, but Series X with Gamepass is my bread and butter console for this gen, with PS5 performing exclusives detail. To give the PS5 it's due - it is quality hardware with a much nicer interface. The pad is better too.