I don't know what everyone keeps yapping about, but Fallout 4's engine has clearly been updated from the previous games. Sure, it's the same engine as Skyrim, and while texture work and geometry is marginally better, lighting and natural effects have made great strides. The game is a lot more stable too (especially after the beta patch). Sure, there are some bugs, crashes and glitches, but it's more stable then previous games.
Too be honest, the biggest flaw of Fallout 4 is easily the lack of real diversity in the DCR song list.
Fun fact: Epic Mickey runs on the same engine (albeit Bethesda runs a custom version of it for their games)







