If the entry title is confusing, that's the level naming scheme for Doom/IoD. "E" stands for "Episode", "M" stands for "Map". E1M5 in IoD is going to be set in a series of mining tunnels, and is certainly the most customized level the game will have to offer, featuring a number of lifts/elevators, a mutagenic river, and a few teleports as well. The music is going to be fast-paced as well; something that'll probably make you want to run faster through the winding claustrophobic tunnels while toasting everything with a Midak Skyblaster.
So why am I hyping all this up? Because I'm finally getting close to finishing design work for it. Honestly, though, it's one of the levels I'm most excited about.