While I certainly have had a few annoying issues myself, full credit to the team behind DevOps (nee VSTS) for doing an amazing job over the last >12 months to overhaul and improve the product. I have been impressed at the pace things are improving.

I have not had the same issues with build machines disappearing into the ether (we use Windows hosts however) but definitely agree that the (lack of) caching is maddening. Our apps are not huge but the NuGet & npm restore times now account for 25-30% of our build time.