What's notable about the second movie is that it's mostly exposition across almost two-thirds of the movie, with the main action taking place only after that.
For newer movies, a lot of spectacle is involved because amounts invested and ticket prices are very high, so producers have to make movies that look expensive and that they hope can generate high payback.
Meanwhile, fans don't know about that, which explains why in the Avatar thread several argue that movies in the franchise are well-made because they made a lot of money, until it reaches a point when viewers realize that they are watching movies that are similar to each other. Given that, more might start moving away, deciding to just wait for the features to appear in streaming (which will happen if producers want to milk franchises as much as they can) or in bargain bins.