>>40196167Dragon Quest - Simple turn based battles
Dragon Quest II - Party system
Dragon Quest III - Class system
Dragon Quest IV - AI system(Forced on you in the original)
Dragon Quest V - Monster recruitment
Dragon Quest VI - Revised class system with monster recruitment(The latter done a bit differently in the remake)
Dragon Quest VII - Class system with monster classes added on.
Dragon Quest VIII - Skill tree system. Alchemy system. Monster team and arena.
Dragon Quest IX - Tweaked class system similar to DQIII mixed with a Skill tree system like DQVIII. Alchemy system.
Dragon Quest X and XI I have yet to play and I'm avoiding spoilers on the latter(Since the former never got an international release, I don't really know what new things would be in it).