Of course Bethesda's Fallout 4 is bigger and better than ever, even if many people don't see a tangible upgrade over its predecessor with some controversy surrounding the omission or change of some of Fallout 3's systems. However, as this is a technical thread, lets strictly talk about that.
Despite looking better than the Fallout 3 (which you should naturally expect from a last-gen ---> current-gen game, the graphics and technical performance leaves a lot to be desired. Even the animations have the same Besthesda trademark jank to them, and in 2015, this is not acceptable, particularly when you look at ambitious open worlds like The Witcher 3 looking much better. Hell, it doesn't even have to look as good as The Witcher 3, but I feel it just needs to reach that current-gen graphical standard. Unfortunately, the Gamebyro/Creation engine does not cut it anymore, and it's clear the consoles (and even some PC's) are struggling in many areas of the game, which should not be the case, particularly in areas where there isn't any strain/demand on the hardware at all.
Whether Bethesda will continue using this engine for the next Elder Scrolls game remains to be seen, but I can guarantee one thing: the reception will be even less amicable if the same problems and issues plague the next game, even if they have been reduced from Bethesda's last game.