It's a lot of work, but there is nothing complicated about getting it done. You tell the art guys the specs and they spend a few days getting all the images and then move on to the next monster.
Why yes, yes I did. But for Doom there were about 10-15 kinds of sprites (monsters, lamps, trash cans). I didn't say it was easy, I said it was straight forward. The code took a lot of time back then, and I'm sure the art guy(s) were busy the whole time.
Indie titles means clever/complicated is better than labour-intensive, because labour-intensive costs money but cleverness just needs one brilliant programmer/artist.
