First to simply define these terms via Google, you all may do the same MMO: A "Massive Multiplayer Online Game" (MMOG, or more commonly, MMO) is an online game with large numbers of players, often hundreds or thousands, on the same server.  MMOs usually feature a huge, persistent open world, although some games differ. RPG: A "Role-Playing Game" is a game in which players assume the roles of characters in a fictional setting. Players take responsibility for acting out these roles within a narrative, either through literal acting, or through a process of structured decision-making regarding character Adventure Game: An "Adventure Game" is a video game in which the player assumes the role of a protagonist in an interactive story driven by exploration and puzzle-solving. The genre's focus on story allows it to draw heavily from other narrative-based media, literature and film, encompassing a wide variety of literary genres ------- Now that that's out of the way, to break things down. To start we'll go MMO which specifically was defined as supporting a LARGE number of players on a server, hundreds to thousands in fact. Destiny only supports 6-9 in PvE and 12 max in PvP. Seeing as Bungie's max players supported per server is barely out of single digits I dont know how anyone could argue Destiny is an MMO --------- As for RPG, as defined the game must support Player choice in character development. You can't choose for your guardian to be good anymore than you can make them evil. You can't choose your alliances, you can't betrayed the Vanguard and join Uldren. There are no character development options. Need I say more? -------- Now Adventure Games "The player assumes the role of a protagonist in an interactive story driven by exploration and puzzle-solving". This in my opinion seems very familiar. There's always open world exploration, and the Story mode has always been sectioned up by missions or more loosely levels. Of course our Guardian is the Protagonist as well. We have no choice but to be the source of good in the story provided My key point though is the focus on Puzzles. There's always a Puzzle in almost every endgame mission Dungeons, Raids, and Exotic quests! Who could forget the Jump Puzzles from King'sFall with the "Pillar" wall, or the Whisper/Zero Hour Jump puzzle Sprint, and how about the Outbreak Prime Quest and the binary code puzzle? Even still we have the jump puzzles up to Morgeth in Last Wish, Plates in Shiro Chi and the newest Jump Puzzle in the Deep Stone Crypt. I know people who still gotta split and come back after the jump puzzles, because they get tough. ------ To conclude the post, Destiny regardless of if it was intended or not is more like an FPS Adventure title than it's claim on being an MMO/RPG title. Agree or not it's entertaining to think about