The main difference which sets Elsword: Shadow of Luna apart is the combat system. Basically, the character will auto-attack, but manual moves are required to dodge attacks. There are 2 additional buttons, one to start a combo attack, the other just an active skill. Auto-attacks will become stronger with more auto-cast skills after each class advancement. Certainly a unique system!
New characters will join players as through story mode progression, though I am not sure if all are available this way. Players are able to bring up to 2 additional characters eventually on their journey and swap between them during combat. There are many costumes for each character as well, giving additional bonuses to stats. There is no launch schedule for Elsword: Shadow of Luna.