Any game that pushes from 2D to 3D is always a good example (or vice versa).
GTA 3 went from top down car racing to 3rd person over the shoulder crime sim.
Zelda Ocarina of Time went 2D to 3D while Breath of the Wild went open world. I would argue Zelda 2 is also a huge change for better or worse.
Super Mario 64 went 3D and revolutionized 3D platformers.
Call of Duty Modern Warfare went to a modern shooter from a WWII series and honed in on multiplayer over campaign.
Monster Hunter World removed tons of loading screens, aimed for more fluid movement, added tons of mechanics and QoL improvements, and allowed moving while shooting for ranged weapons. There’s a clear divide between the “old world” and the “new world” MH games.
Risk of Rain 2 went from a 2D side scroller to a full 3D shooter.
Resident Evil 4 changed from survival horror to more of an action game and RE7 changed it back.
Fallout 3 went to adventure RPG from the isometric CRPG style of 1 and 2.
The Witcher 2 moved from a weird (and imo very bad) almost rhythm-based combat style to more of an action style.
Dawn of War 2 went from a Company of Heroes style RTS to a more hero-focused RTS. It was very hard for me to make the transition.