This game perfectly takes all of the best aspects of the previous 2d games (including samus returns) and makes a great adventure out of it. Backtracking is easier than ever, and often times you will end up on the path to upgrades just because of the level design. First playthrough was 8.5 hours at 100%, and I think that's a reasonable time to expect from the game if you are going in blind.
Can't wait to play it again for that best ending card.