Played up to Lankyroot Jungle so far, which I think is enough time to develop a good opinion on it. I love the game so far, but my once complaint is the backup character. I currently use Anna for debuffs, Matt for attack power, and Natalie for healing/buffing. Lance is balanced with a bit of all three, and so makes a good backup character, but I so far don't have a need for a backup. If someone is low on health, Natalie can just heal them and everything's fine and dandy. On the rare occasion that they run out of MP, they can just eat some food.
I don't blame you for this, though. Having four characters out at the same time seems like too much, but I'd hate to see one of the characters leave for the next game. (Assuming there will be one.)