I like to judge each game in its time context, what other games looked like? better or worse in the same year. Of course within its own series there must be visual progress in 5 or 7 years...
I remember when I first installed Morrowind and Oblivion ... jawdropping visuals for their time. Skyrim not so much, Fallout 3 looked the worst of their games imo at the time of its launch. From the screens and videos (videos only official because I don't want too much spoilers and screens both official and unofficial) I think Fallout 4 is somewhere between Fallout 3 and Skyrim, definitely better looking than Fallout 3 at its release time but failing to match what Skyrim looked like for the year of its release.