Starting a video game franchise might be a hard enough task all on its own, but the real miracle is keeping it going.
A good video game sequel has a ton of plates to keep spinning, arguably even more than when you're making a sequel to a film or book. Not only do the developers have to improve upon the story and characters of the previous entry, but video game sequels also have to improve on the gameplay that drew people in from the start, without being so unrecognizable in terms of design that it does away with what people liked to begin with.
Some game sequels are good, others are - well, we don't talk about the others. But then there are the game sequels that hit that perfect little sweet spot of being such an utter improvement, that it renders not only the original, but however many previous games that came before it, utterly obsolete.
Whether due to length of time or radical alterations to the dev team, these sequels are not only better than their predecessors, they make you cringe just a bit at the thought of going back to them.