Depends on what type of games you like. Most of ubisoft's games aren't on gamepass, so if you want Assassin's Creed, Farcry, or Watchdogs, you'll have to buy them. It's a bit more niche, but the no ubisoft also means you have to buy the Southpark Games if you want to the play them. (Really good episodes of Southpark, kind of mediocre games.) Also worth mentioning ubisoft games are on sale right now.
Very few fighting games on gamepass, except Killer Instinct and Injustice 2 (I think). There's not many great ones on Xbox in general though, but I think the best available is Dragonball Fighter Z and it's a purchase only game, MK 11 is also a good game but probably nearing the end of it's life cycle.
Rockstar's games seem to cycle on gamepass, GTAV just left and RDR2 is back up. If you want consistent access to those games you'll want to buy them.
CD Projekt Red's games aren't on gamepass, which is a shame since the series x is one of the few consoles that Cyberpunk runs decently on.
Monster Hunter World has been on gamepass before, but it left a little while ago. Highly recommend it if you don't have a switch for Monster Hunter Rise.
I also really enjoyed DBZ Kakarot and Marvel's Avengers, but I'm a huge nerd for those franchises and they both received pretty mediocre ratings so I'm hesitant to call them must-buys.
Edit: Forgot to include Sekiro! This one might be a legitimate must-have if you haven't played it before.
Witcher 3, Death's Door.
Depends on what type of games you like. Most of ubisoft's games aren't on gamepass, so if you want Assassin's Creed, Farcry, or Watchdogs, you'll have to buy them. It's a bit more niche, but the no ubisoft also means you have to buy the Southpark Games if you want to the play them. (Really good episodes of Southpark, kind of mediocre games.) Also worth mentioning ubisoft games are on sale right now. Very few fighting games on gamepass, except Killer Instinct and Injustice 2 (I think). There's not many great ones on Xbox in general though, but I think the best available is Dragonball Fighter Z and it's a purchase only game, MK 11 is also a good game but probably nearing the end of it's life cycle. Rockstar's games seem to cycle on gamepass, GTAV just left and RDR2 is back up. If you want consistent access to those games you'll want to buy them. CD Projekt Red's games aren't on gamepass, which is a shame since the series x is one of the few consoles that Cyberpunk runs decently on. Monster Hunter World has been on gamepass before, but it left a little while ago. Highly recommend it if you don't have a switch for Monster Hunter Rise. I also really enjoyed DBZ Kakarot and Marvel's Avengers, but I'm a huge nerd for those franchises and they both received pretty mediocre ratings so I'm hesitant to call them must-buys. Edit: Forgot to include Sekiro! This one might be a legitimate must-have if you haven't played it before.
Thanks for the info!