Yay Escape!

So, i signed on to do a doom clone – i was hoping for escape, because now I can make a system of rising lava to act as a timer for getting out of each level. My game idea is pretty simple:

1) level is full of monsters which shoot or charge you
2) you must find keys to unlock doors. Expect ambushes.
3) When you get to the final switch, you must flick it to open the door
4) The lava starts to rise!
5) GTFO before you burn and die.

I plan to have 3 enemies:

1) Lava Monster – throws lava at you.
2) Sniper – static, hides behind cover, can only be hit when he is about to shoot you.
3) Flying Moustache – is a moustache which flies. Obviously.

I’m hoping I can make enough levels – I’m thinking it will be easier to do a few large levels than many small ones.

Who likes this plan? Any suggestions? I’ve already started.