The biggest contention I have read from some of the online opinion makers is that the band evolved from a twee Byrds/shambling band that eventually eventually into the loud swirly tornado of bliss noise that made Isn't Everything and Loveless.
It seems some of those people maybe expected the band to go into another evolution. After all, it has been two decades and all that. In interview through the years MBV masterbrain Kevin Shields has mentioned many different things that he had gotten into musically and stylistically since Loveless came out and perhaps it was hoped some of those things would be integrated into the band's sound rather than sounding like they are standing in the same place. It would have been funny if the band would have taken some weird detour just to see how people would complain (and there are some that are going to complain no matter what) because then it would sound nothing like the band they remember.
Some bands who haven't done records in ages have released ones that are decent to really good (Vaselines, Bailter Space, the Feelies, Subsonics fer instance) that sounded they way people knew and remembered them but still had enough fire, energy or cleverness not to sound too much like complete good times/great oldies, let me see if those clothes I wore back in the day when I could really afford to eat 3 square meals a day (but, for some reason, always had beer money) still thing. There wasn't as much expectation or hype around those records as there has been for the new MBV and that's why there have been some really polarized opinions on it so far.
The band will always have it's blurb in the rock-n-roll history books if, for nothing else, nearly bankrupting it's record label Creation. The rock-doc on the label, Upside Down, is now available in it's entirety on YouTube (and posted above here). It doesn't really touch on that part of the story much but is still an cool watch for people into music history of more recent decade.