I think Russ did an unusually good job of explaining the ideas around vgo, grounded by using real world examples. He set a high bar there, but hopefully Sam adopts some of the same methods of very concrete examples to explain his criticisms.
As it stands this is an interesting piece of reading but is too high level and abstract in its criticism to be effective. Looking forward to future installments that hopefully that will make Sam's criticisms clear.
From what I can tell one piece of criticism is the inability of vgo to define incompatibilities. That is that if you know these versions won't work, you can say never allow that version in your dependency graph. I'd love to hear more examples of this in the real world. Since vgo dependencies are basically always "pinned" this seems like that not big a deal to me, but maybe I'm missing something. Perhaps this is something that occurs with having two of your dependencies having different dependencies on a third package and one of those works only with dep3@v1.2 and the other only works with dep3@v1.3 or somesuch.
Maybe there are ways around that or maybe that's not the actual problem (again, hope Sam explains more in the future). I think there is a really interesting element to MSV that will actually drive Go culture though (and I'm a big believer in the importance of the culture of a language) which I think may minimize the problems that Sam is talking about and for the betterment of the community.
As others have noted, I hope that Sam comes out with the rest of this series quickly so that the go community can commit do a direction sooner rather than later and move on to actually building this new ecosystem.