I'm always perplexed when I encounter someone making claims that indicate they honestly believe they have "finished" it. I suppose what is one person's "fun replay" is another person's "tedium" . . . but you did ask "is it over?" so I do feel it is warranted to point out that: based on my experience with the game, totally in the ball park of 400 perhaps 500 hours (I leave Steam offline and I have not tabulated total hours played across all characters for several weeks, since I was very near 300 hours) it is inconceivable that you have "done everything there is to do in the game."
Now granted, much of what there is "to do" is, when considered as individual actions, observations or experiences, relatively inconsequential if not esoteric. However, when these thousands of "things to do" are taken in the aggregate, and considered as elements in possible permutations with varying themes of play or character builds, the aesthetic possibilities are virtually limitless and even the functional possibilities are quite large in number.
Every time I shelf a particular character and start over, I experience different things in this game, ranging from such mundane things as: noting an entry way, stairwell and passageway that allows me to get to an unmarked location I had never accessed before; encountering an NPC I had never encountered before; exploring an alternate theme of interaction with an NPC; exploring the effects of various companions in different play styles; exploring perks I had never taken before; exploring underwater; exploring as much as humanly possible an entire area, meaning TRULY looking at every visible portion of a small portion of the land from every possible angle . . . and finding stuff that had been laying there all the time but which I had just tromped passed dozens of times . . . and then realizing that Bethesda did this with this entire map . . .
If you really feel "it is done" then no one should presume to instruct you otherwise. But it almost seems you are feeling more 'lost' than 'over it' and wondering aloud "Is there more to do?"
I would say, if a particular character is feeling "done" then archive the save files, reroll a new toon witha new concept and play a different way. Mods are not necessary to simply change playstyle dramatically. Ideas:
1. A 10 INT build
2. A 10 CHAR build
3. A 10 END build
4. A 10 PER build
5. A 10 Luck build
6. A 10 AGI build
7. A 10 STR build (that does not use heavy weapons or power armor since those are so obvious).
8. The myriad of "builds" that lie in the spaces between those extremes
9. A build that makes no use of settlements whatsoever
10. A build that makes no use of firearms or lasers whatsoever
11. A build that relies on non-lethal force as much as possible (syringer)
12. A build that relies on stealth and melee
13. A build that relies on luck and perception
14. A build that has an agenda of some sort (e.g., hates BoS, or loves BoS [and makes a beeline to do ALL of their quest first and without doing ANY others . . . or just replace "BoS" with any other faction, or with "No Factions")
Just off the top of my head . . .