Assassin's Creed III
Now that I've recruited trainee Assassins from the districts of Boston and New York, liberated all the colonies from Templar control, swept the Atlantic of enemy ships, found Captain Kidd's lost treasure, built up a safe, secluded homestead, and debunked a hunter's wilderness myths; now, I think I've completed AC3 to satisfaction.
Some of the optional content, like the naval battles and Daniel Boone's tall tales, is surprisingly entertaining; while of course some, like collecting a bajillion bird feathers and almanac pages, is pretty menial. As in the franchise's last few installments, there's no shortage of choice in terms of what (if any) extras you decide to throw yourself into.
For the record, I put a little over 20 hours into AC3 doing barely any of these extras, and ended a little under 40 hours, having done the ones I found interesting. So, pretty good longevity on this guy.
Progress: 75% completion