FWIW: the guys behind Miner Wars (Keen Software House) are working on a new game, Space Engineers, which has full 3D, Decent-like movement. The game is more about construction than combat, though weapons exist in the game. It's currently in beta, but they have been consistently cranking out weekly updates. One of the more tantalizing features they want to add: in-game C# scripting so players can automate a lot of the functionality and build their own communications systems.