I'm Making a Build/Sandbox Map. What do you look for in them?

It'll be loosely in the style of gm_construct, but has more going on already like excess construct and all the other big spinoffs. There's a lot more I want to add still but already having compile problems so might have to leave a lot out, and I'm not sure what to prioritize. It's been quite a few years since I played sandbox to build anything serious, but what do people play sandbox for generally now?

As in, what would you be looking for?

• gm_construct style buildings? or other buildings more suited to simple roleplaying?
• large flat open space?
• water? in what forms and how deep?
• vehicle infrastructure? so roads, rails, garages
• tall skybox for aircraft?
• whatever works for nextbots or NPC battles?
• secrets or things to explore?
• spawn with teleporters to useful locations?
• anything else I missed?

You can assume AI nodes and navmesh will always be included, because I've never seen a situation where they limit the possible size of a map.