Interconnected and realism themed vanilla-ish level design. Different difficulty setting. Single or co-op 2-4 players. No advanced engine needed. No jumping needed. Falling damage may kill you. Has official OST addon. May crash in some DOS engines like Chocolate Doom or Steam's DOSBox due to large level design areas. Tested and works fine in Crispy Doom and PrBoom+.
These are my final words about the process of making Bloodline. The final version is 52d-3