1. good writing
2. good characters
3. good worldbuilding
4. SPECIAL
5. classic style dialogue box
6. more new creatures with new names (there's like 10 different "mirelurks")
7. better voice actors
8. better combat (under the surface fo4's combat is a downgrade)
9. follows the lore reasonably well (external consistency)
10. internal consistency
11. interesting conflict
that's about it really. all the stuff that should be in a fallout game and was in NV really. I'm not a asking much. I think fallout 4 really only had no. 11 but that's negligable, at least for me, because of a lack of numbers 1, 2, &, 3 which all go hand-in-hand with no.11. no. 11 is nothing without 1, 2, &, 3.
fallout 4 is especially disgraceful when it comes to numbers 9 & 10.