I like making Thief fan missions, despite or maybe even because of the Dark Engine's age. One quickly learns to work with the engine's limitations rather than against them.
For my 2.5D Adventure Mental Repairs, Inc. I created and rendered the backgrounds in 3ds Max. The game takes place in an office building, and the player can access two floors via elevator. Since there is a crazy computer on the top floor, I took some inspiration from the sci-fi classic Tron for its design (see Dillinger's office).
For the ReWrap Short I rebuilt a small dungeon level from Bethesda's Oblivion in 3ds Max without using any of the game's assets.