IGOUGO, still using RPG stats in what's become a very large scale game, giving things huge numbers of wounds because you made guns that can do huge amounts of damage, rather than literally any other solution with less book-keeping, speaking of books, the rules for most factions being spread across multiple $80 books, and the convoluted mess of "gotcha" stratagems etc that few players can reasonably remember or plan for due to sheer volume, leading to a lot of "feelsbad" moments rather than the fun twists I think they were supposed to be.
I'd say those are the biggest.