I've avoided this thread for a bit because I assumed there'd be a bunch of dick jokes. I was pleasantly surprised with a bunch of thoughtful and awesome comments. Fucking love the nerdiness of this community.
To answer the question - there's a number of them, but i think the first one for me was Fable: The Lost Chapters. It added a ton of new content on top of the base game, plus there were a good amount of extra side quests, challenges, puzzles, collectibles, etc, that I got so much beautiful and memorable gameplay from it.
It does feel like games nowadays are made to appeal to the masses and/or pump out a lot of games as quickly as possible in order to generate as much money as possible. Fortunately indie game studios and devs still exist for people that are looking for a little more substance. Shout out to the Indie Stone for Project Zomboid and their continued efforts to add more awesome features to their game!!