Kingdom Rush is the tower defense game, but the duration/replay value isn't good (imo)...maybe there could be a 'Kingdom Rush' game without the actual 'Kingdom Rush'/heavy-duty game part? It'd be the same cartoonish Kingdom Rush stuff, but it'd be a puzzle/trajectory/etc game like Candy Crush or Angry Birds (games that are simple that have many many levels). Maybe 'heroes' and 'enemies' and 'towers' and 'abilities' and all the heavy-duty in-game mechanisms could just become 'combos' like an 'Archer/Magus/Weirdwood combo' or 'Karkinos combo'. Simpler stuff. There could still be spells and little heroes.
Something easy to produce that could be produced more often? For iOS not PC? I don't know.