I want more areas to explore, with wider variation.
All we have now is edited versions of the normal underground and normal overworld. Corruption is slightly different because there's holes everywhere. Apart from that there's no difference while exploring.
Underground corruption + hallow is even worse because they're just caverns filled with ebonstone and pearlstone.
We need stuff like castles/towers, underground temples, pyramids, etc.
More areas that are different to explore.