The difference between Rayman and Rayman 2 is startling, and I find it strange it's rarely mentioned in these types of threads, because of it wasn't for having the same main character they would be two different games, not just in formula, but in music in level design, and the entire lore and worlds are completely different and have no connection to each other
Rayman 2 may as well have been a reboot, and there's 5 releases of the game that all have differences from each other, some significant.
Then you have Pacman 2 vs. Pacman which is another "sequel" which is very different from the first game. Going from Pacman to a pseudo-point and click adventure game with a sling shot with large characters and an int7eractive world was crazy.