Series/Franchise milking the most out of people?

River City Ransom is one that they could've made roughly 7 sequels off of. Everybody here is raving about Dungeon Fighter, but River City Ransom is almost exactly the same thing... in 8 bit.

That game was awesome. It was also hilarious how it had a whole "rpg" growth scheme to it, yet you could easily beat the final boss almost right away because he just sat there and took the beating while telling you he's badass.