So I've been playing The Cult of the Lamb, the indie smash hit darling that is already trending on Twitter here in Germany, and it's pretty obvious that it takes heavy inspiration from The Binding of Isaac (BoI)
The game is split into two modes: crusading and building your cult. During crusades, you smash heretics and grab their stuff, which you then need to use to build up your cult. It is, to nobody's surprise, extremely compelling. I've been making games for twenty years now, so it's hard for one game to really grab my attention, but this morning I started playing and when I looked at the clock, somehow an hour had evaporated??
Anyway, the crusade gameplay is extremely similar to BoI, but only at a cursory glance. When you enter a room, the doors close, and they open only when all enemies are defeated. Rooms are connected in cardinal directions. There are shops and sacrifice rooms, and there's a little restaurant too. Your health is measured in hearts, with each enemy doing about half a heart of damage. You can collect blue hearts, which don't regenerate, and black hearts, which damage all enemies in the room. And you beat each floor by fighting a miniboss. There are even tarot cards that give you special abilities!
But that's about where the comparisons end. Because Lamb and Isaac are telling completely different stories with their gameplay. Isaac is about a boy who is locked into a cellar by his unhinged mother, fighting personifications of grief and guilt with his literal tears. But Lamb is about the Chosen Messiah of an Eldritch Horror, who tasks you with building a cult to worship and defeat the Old Gods who have imprisoned him. Your magic is called Curses and you go on literal crusades!
Isaac asks: How much are you willing to change yourself to defeat your Mother? But Lamb asks: Since every God is horrible anyway, why not join the winning side?
I think this game proves a broader point that game designers have to make time and time again. Not only is it okay to steal mechanics from other games, it is your imperative to do so. Because designing a game is more like making a soup: Every ingredient adds its own texture.