In part he is dead on.
hg really can't handle large repositories; but to be honest if you're working with GB's of data then you're using the wrong tool :) period.
Point two is a "complaint" I agree with. The repository structure isn't particularly good - it "works" for the most part but sometimes you just want to kick it. And forget hacking around with it..
Silly things like "hg copy [file]" doesn't copy file history but does a remove/add & cp/rm are another ball ache.
Ultimately hg is a good tool; for lightweight, hackerish version control it is great. Beyond that? Yeh, use Git.