I suggest a discussion on this because I have no idea how to make it more interesting :/
You enter what apears to be a abandoned habitat.
----- Level contatning small rooms (each with former sergeant or former human), long corridors (chaingunners) and security posts (former commandos)
Pure evil is lurking beneath...
----- Level is spawned with an unique weapon, or advanced weapons with two mods. Time is of the essence. When you enter a level, the timer is started and goes down your every move (not every second!). When you finally get the weapon, the current timer value is halved. When the timer goes off, monsters start teleporting in. This can go on forever. Note that when you enter this level, you have to quit it, otherwise your chance to get the 100% kills score is very slim.
This level is simple... Dead simple... (special level)
----- Level with a number of pillars, surounded by a thick wall. The pillar themselves are indestructible. As the time flows, they will lower and reveal mancubi hiding behind them. On the first three difficulty levels, you have to kill all of the mancubi. After that, the wall sorrounding the pillars also gets lowered, revealing arachnotrons. On Difficulty 4 or 5, after killing the first mancubi the wall gets lowered instantly...
Feels like I've been here before...
----- You enter a level that you had just demolished, how is that possible? No time to think, you have to prepare yourself... Ah. all the enemies are dead. Well, not for long, because the corpses will rise again, after some time. This time, you have to gib them (gibbing will be implemented?) to make sure they don't rise by themselves again.
You feel out of yourself
----- Level contains many teleports, but only monsters can use them