Adds more depth, fun challenges and chase goals for factorio addicts, especially in the later stages of the game. Intended to be a high quality vanilla+ experience and the ideal version to megabase on.
Coal is a pretty valuable resource and I feel that if you have to use it to get "more efficient" iron to steel recipe it should give 5 instead of 4. This would push it over the edge to warrant the complexity upgrade and the resources needed.
The intermediate carbon + iron plate recipe is 25% faster on steel furnaces which are themselves x2 speed, and you get 20% productivity on the plate recipe, so I think balance is fine.
However while checking the numbers out I noticed I forgot to make it benefit from the steel productivity upgrades (not that it matters much, as you probably moved to the foundry recipe by then).
