After spending about 80 hours into FO4 I decided to actually play the FO3 GOY edition I bought long ago and never played.
Finding FO3 much harder. The constant degradation of weapons and armor was killing me and my caps so I downloaded a mod to prevent that. REALLY helps.
The games are very similar, I feel like I've got a bunch more FO4 to play but without settlement building and the load times are nearly nonexistent. I hear New Vegas is better than FO3 and I have that too.
Go back if you didn't do FO3!! I'm kinda glad I blew it off until now.
I loved FO3. Couldn't get into NV.