To do so, I've done the following thought experiment: Imagine Fallout 4 being remade in the Fallout 3 engine. Including the world, quests, characters, dialogue wheel and gameplay mechanics (respawning enemies, legendaries, invincible companions, resetting locations). What I'm trying to say is and whether it be realistic or not - would the world and quests of Fallout 4 in the Fallout 3 engine be considered a good game without the new fancy gunplay, power armor, modifications and Workshop? Definitely great additions to the game, but still. Would it be fun to roam around in the world of F4 in the Fallout 3 engine, doing that Workshop quests that sent you to random locations so you can clear everything in there out. Would it be fun to have so little influence towards the factions and locations? Would it be fun to not being able to play an evil character as well as not being able to kill all those Essential NPC's?
The world of Fallout 3 being remade in F4's engine (including all the additions) on the other hand would be one of the best gameplay experiences ever imo.