What really has me interested in this game (despite feeling rather ho-hum about EO) is how the recruiting and fusing demons will be progressively and constantly keeping the gameplay fresh, giving the player plenty of new tactical options throughout the game as the s/he'd progress through it.
One of the things I didn't like about EO was how restrictive it was about setting up characters into specific roles (you'd specialize chars into specific roles, and they'd be pretty restrictive roles). While the game offered a lot of options between and within the classes, changing options/roles would be pretty time-consuming (creating a new char, losing 10 levels to respec). Just not appealing features to someone who just wanted to get through the game at a good pace, but still have room to experiment rather than being shoehorned into specific roles. I'm hoping the demons in SD will remove those annoyances for me.