1 day and 1 evening (bad game, made me stay up until 1 AM yesterday... *sigh* I'm in the office and I'm dead LOL).
I'm level 15 and I actually spend the first 6 levels just building Sanctuary (doing the Concord thing and exploring a little bit, but after reading that this game is hard and the combat is more realistic, I got scared and just started to scrap and build stuff around "home") LOL I finally made it to Diamond City last night and I like it. I also saw my first trader in Sanctuary yesterday! The Pack Brahmin was kind of stuck on the way out of town, so I had to remove a fence part and build a gate.
I have discovered and cleared quite a few locations so far. And I found a real combat shotgun and sniper rifle that are now modded to be mighty powerful.
Love the modding/crafting system.
So yea, I have FO4 on my mind for sure. I'm having a blast exploring the world, crafting and building up my various settlements.