Cthulu Saves the World finds its feet much faster than its predecessor. It's immediately clear who Cthulu is and what his motivations are. And a dread monster who wants to become a "true hero" in order to unlock his sealed powers is a much stronger comic conceit than whatever was going on in Breath of Death VII. Your party is weirder and the incidental NPC dialogue is more entertaining and diverse.
In terms of gameplay, though, the games are essentially the same. Cthulu Saves the World is a little more ambitious in terms of things like specialized equipment (I recently found a sword that had a lower base attack power, but did greater damage to undead, for example), but the fundamentals have not changed. You still have to build up a combo by landing attacks and then deal massive damage by using your combo-finisher move. You can still camp at a save point and exhaust all of a dungeon's encounters. However, the Breath of Death VII formula works pretty well, so I see no great need to change it.
Overall, I'd say I'm much more entertained by Cthulu Saves the World. It feels more . . . confident, somehow. It's only natural, of course. As a follow-up game, it benefited from increased experience, and probably an increased budget. That it's based on a stronger fundamental idea is probably a coincidence, though.