From August 2000 till December 2001 I worked at Rebel Act Studios. First as Game Designer on a project that was sadly cancelled, and after that, as a Level Designer and Scripter for Ultimate Blade of Darkness.
This game was an XBox version of the PC game Blade: the Edge of Darkness (Also known as Severance: Blade of Darkness in US). But it was more that a simple port to the XBox. We rewrited the story, rearranged the levels, edited the old ones and added new ones.
We had an in-house editor to build the levels, called LED. It worked as a substractive editor, carving the rooms in the game world. We had a 2D interface, and the rooms were defined by their vertex and the height associated to them. You were eble to define if you wanted a flat roof for that room or a curved one. That means most of the time we had no idea of what the final result would be till we render one view. This is how the editor window looked like:
Sadly, Rebel Act Studios closed before it could be released.