Gamers really don't ask much. If those things make up fun playable game it is enough to be popular. I have understood it might be formulaic, but it is well executed.

In the end you could ask same thing about any art. Music is just same notes arranged differently, sometimes with voice lines over it, instruments are mostly same. Movies, pretty much same plot points and similar characters. Same goes for TV shows and books... And all of them are popular.