Here's some of my thoughts from my play so far. Maybe I'm blaspheming by suggesting things like this; apologies if so, but figured I say them anyway.
A. I think I'd like to see DoomRL have much bigger levels. They really do feel too short to me at the moment.
B. Also, a chunk of the generated maps don't really ~feel~ like levels from Doom? I almost feel they need more empty space, and perhaps a few setpieces (i.e. having more vaults created by people inserted into levels) as well as the secret levels that are already there. Even if this is as an Angel challenge (Angel of Real Estate?). :D
C. More than one active character. I typically have like 8 characters on the go at once in Crawl, for example. Because I'm nuts. Of course, this would ideally have to go hand in hand with save and exit anywhere, rather than just the stairs.
D. Some n00b medals. Iron Medals, or something. Most of the Bronze ones seem too intimidating to me, never mind the higher up ranks.
Basically, its great at the moment, I just feel its scope could be more epic.