There have been a lot of Dark Souls games since the franchise made it big with the first game, which only came out in 2011. From Software are now gearing up for Dark Souls 3's release, coming just a year after Bloodborne, which took from the Souls series pretty liberally.
According to game designer and president of From Software, Hidetaka Miyazaki, you probably shouldn't worry about the franchise getting run into the ground though. In a recent interview with GameSpot, the designer said quite plainly, that we probably wont get another game in the series:
It'd be a lie if I said I have no concerns about that. I don't think it'd be the right choice to continue indefinitely creating Souls and Bloodborne games. I'm considering Dark Souls 3 to be the big closure on the series. That's not just limited to me, but From Software and myself together want to aggressively make new things in the future. Dark Souls 3 will mark the last game where the development project began before I became president.
Continuing on, talking about the future of the company, Miyazaki said:
The next title will be a game that was conceived while I was president. I believe that From Software has to create new things. There will be new types of games coming from us, and Dark Souls 3 is an important marker in the evolution of From Software.
This sounds like a good idea. I'm sure there is enough demand for another Dark Souls game, but there is most certainly a fatigue building around the series. I really do believe that From Software are gifted developers though, so I want to see their talents applied to other genres and ideas. This gets a thumbs up form me.