Very old example, but Zelda II: The adventure of Link.

It’s a very, VERY, different game compared to the first Zelda.

The NES Mario and Zelda games. Such strange transitions on both accounts, although I think Mario 2 has aged better (and is better), I just never liked Adventure of Link much.

Darksiders basically changes genre with every game. I’d say it’s the definitive answer to this.

Fire Emblem changes secondary mechanics and storytelling so often that it’s led to a fanbase that doesn’t agree on much of anything.

Guild Wars 2’s only real commonalities with GW1 are the world and horizontal progression.

Assassin’s Creed became a poor man’s Witcher 3.

Diablo changed drastically between entries.

Shining has run the gamut of first person dungeon crawlers, strategy RPGs, and action RPGs.