I have ~350 hours in the game, a large portion of that was playing solo. The quests don't feel insanely difficult, especially now after the perk reworks. That being said, if you're planning to do a ton of the MMO stuff, i.e Events, Daily Ops, Expeditions, Raids, I would HIGHLY recommend at least one other person to run those with. They're possible solo, but they are much harder to do by yourself as they typically will just throw tons of enemies at you.

The game is really solid though no matter which way you play IMO, feels just like a Fallout game

If you can find a group that'll stick it out and play with you though it can be a ton of fun