define "finish" :D
Finished the main quest line and most major side quests in Oblivion, Fallout 3, Fallout NV, Skyrim, and Fallout 4. Fairly completionist in Fallout 3, NV, Skyrim, and *most* of Fallout 4. Some small collection/completionists stuff I didn't do in Oblivion and Fallout 4.
I'm sure there's still some undiscovered caves, dungeons, or side quests I missed in most of them, but I put 100+ hours into Skyrim, FO4, FO3, FO:NV, and at that point I think that's pretty much finding everything I could.
I remember like 100+ hours into Skyrim I stumbled into blackreach after not exploring it much in the main quest and was like "Jesus christ this is too big for me ...."