I didn't like Morrowind. I didn't bother playing Oblivion. I didn't like Fallout 3 (despite or perhaps because of being a hardcoe old school Fallout fan) and I couldn't really get into Skyrim.
But I think they actually got it right (if not perfect) this time, and I'd like to offer my congratulations, and also some thoughts.
Stuff I liked:
-Settlements
-Power Armor
-Main story
-Piecewise armor
Stuff I disliked:
"Fake difficulty" in settlement management (it's hard to tell what your settlers are doing, or find them to give them tasks, and they'll starve rather than tend the plants without specific instructions.)
Stuff I'd like to see more of:
-Magnolia
-Music (Finding a cache of prewar music would make for a cool quest)
-Guns (more types, more mods.) Particularly, but not only, the iconic Fallout guns that are missing, such as the 10mm SMG.
-Actually different monsters (as opposed to different flavors of the same monsters.)
-Sorting options for Pip-boy inventory screen (val/wt would be seriously handy.)
-Uses for the 20+ Power Armor frames I've collected in my garage at Sanctuary Hills.
-USS Constitution/Captain Ironsides
And stuff I'd like to see that isn't there:
-Crafting guns/armor and ammo (rather than just modding guns and scavving/buying ammo)
-A way to chamber a gun in a different caliber *and* change it between semi and auto.
-Multi-type ammo system (like NV)
-Felicia Day
-Chrysalis Motors Highwayman
-Centaurs? I mean, they're disgusting and I hate them, but what's Fallout without Centaurs?
-Multiplayer?
-The ability to claim a bed at one of my settlements, and to permanently assign a bed to each of my companions who need one.
-Offhand melee weapons/shields.
-Better keybinding for PC.
-Better handling of existing structure and terrain for Settlements. If there's a wall or floor I can't scrap, I want to be able to repair it or otherwise work with it. If there's a doorway, I want to be able to put a door in it.
Revisiting the Capitol Wasteland could also be fun. Could be interesting to see what's changed in the last decade or so.