Avatar was at least more memorable than the majority of the garbage that are able to gross over a billion dollar worldwide these days.
Not sure about memorable, but it deserved more to do what it did than most Billion grossers did, that's true. As an experience, Avatar was also ace, which is why i'm hoping for the best regarding the sequels and expanded unvierse material.
The thing with Avatar though, is that it was one of the highest grossing films of all time, but doesn't seem to have generated as much of a following as the likes of Star Wars, Jurassic Park or Titanic. If we put things in perspective, it's not as if other "popular nerdy films" are more talked about either, Abrams's first Star Trek was more memorable either, the Marvel films are usualy brought up mostly due to the constantly released films set in the MCU, not exactly due to the craft behind them, etc.
It's difficult to name a film that came out around Avatar's time that is more talked about, Batman Begins and The Dark Knight maybe, Inception definitely, Tarantino's last 2 films too. When everything is put into perspective, Avatar's not exactly as forgotten as other films geeky fandoms like to embrace.
The reason "Who remembers Avatar?" has become such a popular joke is due to various reasons, one of them is James Cameron's cockiness and arrogance due to achieving such a giant success, another is the already mentioned fact of it not being as often talked about as the likes of Star Wars and Jurassic Park, and finaly, there's the easy to make fun of lore, which has gotten a bit cheesier as time went by.
