James Cameron has a lot of new gimmicks up in his sleeve:
Kid actors/kid blue aliens, Kate Winslet as a blue alien, underwater motion capture (this alone is a huge gimmick), underwater scenes/oceans of the alien world, etc.
This movie will have lots of novelty and brand new CGI gimmicks that will probably create another bandwagon of casual moviegoers and people who don't usually go to the cinema that will watch this 10 times, spread positive wom, etc. since it's never been seen before and everyone will want to experience the new and improved CGI and share it with family and friends....kinda like the first one lol
Especially since this one will focus on family and will actually have kid characters, possibly making it more 4-quad than the first one (wow)
The long wait could actually help it and make it seem more of a once in a decade event film, actually that's probably how Disney will market it
In my mind, A2 will be the next highest grossing movie of all time WW (not sure about domestic though, it might be a Jurassic Park type situation)
As for A3, A4, A5...idgaf about them for now