The Phantom Pain is to be the Last Metal Gear Solid
In an interview with IGN, creator Hideo Kojima claims Metal Gear is over:
I always say 'this will be my last Metal Gear,' but the games in the series that I've personally designed and produced -- Metal Gear on MSX, MG2, MGS1, 2, 3, 4, Peace Walker, and now MGSV -- are what constitute a single 'Metal Gear Saga.' With MGSV, I'm finally closing the loop on that saga. In that sense, this will be the final 'Metal Gear Solid.' Even if the 'Metal Gear' franchise continues, this is the last 'Metal Gear.'
To be fair, this isn't the first time he's said this. Kojima's been trying to get away from the series since Metal Gear Solid 2, but he was forced to go back when MGS3 wasn't going well.