I think it's one of those games which are greater than the sum of its parts. Take mission design, for example. There's criticism about repetition, specially on side missions, or lack of unique stages, in the way previous games or Ground Zeroes had. On the other hand, every mission can be tackled in many different ways, and with secondary targets to spare, it's ever inviting us, to come back and play again. Mother Base took this design to its limits: every invasion shares a pattern, but so many things can go differently, that every match feels unique.
Modern Hitman does similar with Contracts. Well, The Phantom Pain gave its own spin to the idea, in an open-world, continuous environment. The sad thing in this story is there won't be an evolution of the concept, within MGS. Hopefully, Death Stranding will be able to raise the ante.