I can easily see Fallout 4 beating Skyrim on all fronts. Fallout started building a following what seems to me like 20 years ago when it first was introduced after that movie A boy and his dog and most of the people I know that played it back then are still playing it today on top of all the people that have started playing it since.
The fan base for Fallout is already there and bigger than the Elder Scrolls crowd, the series didn't just pop into existence with Fallout 3.
Its a borderline cult that spans at least 3 generations of players and has had people sitting on the edge of their seat in anticipation of the next installment since 2010.
This is one of those questions like "Is water wet?", "Can you breath air?", the answer is already obvious before the question is even asked. A more interesting question would be something "So how many other game companies do you think will go broke from their big release because who wants it if they own a copy of Fallout 4?"
On a foot note, and as example, on the day after the Fallout 4 release announcement, digital sales of Fallout 3 and Fallout New Vegas both jumped roughly 1,175%. Just the sales of those previous versions outdid the pre-order numbers of any upcoming game to be released this season.
I wished I owned stock in BGS because their going to make cash by the buckets off this for years.
As far as critic numbers, critics are generally self-proclaimed experts who generally know very little about the subject they are voicing an opinion on, and just as a rule of thumb should be ignored since if they like Mario-Cart, their going to give bad ratings to any game that isn't Mario-Cart.