Followed by a sequel, Apventure to Atlantis. I played Odyssey for hours when I was a kid - and I still love firing it up when I find it on an emulator. The game expanded on two earlier games, Dungeon Campaign and Wilderness Campaign, both of which predated Atari's "Adventure" by a couple of years. Odyssey was a true pioneering game, predating the likes of Ultima.
I dispute the statement that it was the first graphic adventure game. Perhaps for consoles, but there had been graphic adventures made for home computer systems such as Apple II for several years before Adventure came out. Examples include Akalabeth: World of Doom from 1979. There were also several released in 1980 such as Odyssey the Compleat Apventure and Mystery House but I don't know if they came out before or after Adventure. The guy who did Odyssey also did something called Dungeon Campaign or Dungeon Adventure in 1978 that basically had everything Atari's Adventure did other than monsters.