After seeing what this thread has said it has to be down to eveyones expectations. I didn't have any cos i was just getting back into gaming and didn't see the build up, so no expectations dashed.
IMO, most (i said most, not all!) current needs of gamers, like us lot, want 2 things broadly; multiplayer and choice.
Destiny gives that, now more than ever (coupled with its simple gameplay). I wouldn't play this if I wasn't lucky enough to find the FG clan through stretch - 4 workmates raved about this, loved it and quickly stopped playing cos they didn't appreciate the 2 aspects above.
It'd be great if you got brand new scenery each time DLC come out, amazing graphics, new enemies, etc but thats not the gaming world now. WoW can't be compared to this - its made in such a different way and in an era that we got too used to getting more for your base game. Look at other games now and they are v.similar.
TLDR: Original expectations never met, we all want MP and choice - Destiny is simple and gives that (now after this ex pack)