Iikka Keränen, former Doom level god and currently employed at Looking Glass, has been interviewed at A Focus On Levels. For those of you who wish to learn about important aspects of level design this is a must-read. An excerpt:
The only thing that inhibits design is that many people get lost in all the visual-technical goop and forget to actually design what they do. Building aesthetically pleasing shapes and proportions is not dependent on what engine you're working on, nor is good gameplay as long as the game itself is good.
Read! Learn! Multiply! Also thanks to Ola Björling for the link.