Very nice for a first!
Decent brushwork and lighting, nice game flow and monster population, sticking to one theme... very good!
One little thing for improvement: sometimes monsters can be caught behind the elaborate doorframes and arches. If they get stuck, they will be harmless, and can be gunned down with no risk. May i suggest adding a few 'noclip' brushes to guide the monsters?
Very nice! Another mapper i have expectations for...
Thanks for your work, and thanks for sharing!