I was trying to think of which games created certain mechanics that became popular and copied by future games in the industry.
The most famous one that comes to my mind is Assassin’s Creed, with the tower climbing for map information.
Skyrim for the horse armor dlc.
I remember them having a sale on Oblivion DLC one time where the rest of the DLC was half-off, but the horse armor was double.
Oblivion was weird on DLC. Knights of the Nine was pretty good, and Shivering Isles was amazing. But they also had bullshit stuff like Horse Armour.
That was Oblivion believe it or not. Ahh, the good ol’ days where everyone got up in arms over even cosmetic DLC.
I thought that the uproar about horse armor was that it was the first pay-to-win DLC. The armor was not just cosmetic but actually provided a stat boost to your horse. The accusation was that the developers had made it too easy for enemies to kill your horse and decided to patch the game to fix it but made players pay for the patch.