A small probably non-spoilery thing I discovered not long ago.
Apparently you do not drown when using power armor. But you cannot swim either.
But walking under water is kind of interesting.
As far as I know though.. Bethesda have not done much about under water stuff.
A shame really.
I noticed that. I don't know if the jet pack works under water though, I probably tested it and forgot the results.
Did anyone play with the jetpack? It eats through the fusion core energy much like sprinting. After I get 10 charisma I'll focus all my level ups on the perk that, on last rank, doubles the duration of fusion cores.
I had to battle three dudes with power armors plus two crazy melee dudes and someone on a tower with a fat man AND a rocket launcher. So sprinting around and jumping to/from buildings was fucking amazing. They'd take cover behind a building, I'd just impact land on their heads and shotgun whatever was left.
End of the battle both my legs were destroyed and arms were on red.
Problem is all the great fun Power Armor perks is dozens of level-ups away from me. I focused completely on crafting, settlement, and hacking/lockpicking
On another note, give a certain 'medieval' costume from a comic character, and a certain 'flaming sword' to a follower, and watch as you can't figure out if you're playing Fallout 4 or Elder Scrolls VI.
PS: About water stuff, I had heard Beth DID make some underwater stuff - that's why the Aquaboy perk is a thing.
However, I found no suggestions or evidence of that in-game. Didn't explore much under water, though.