If you haven't found it already, this editor guide is great: http://infosuite.duke4.net/

Or even better:
http://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=223542709

Thanks for your referrals to that guide Mateos. It really is a superset of everything you need to learn how to map, anyone posting links to individual guides aren't giving the full picture, even guides as awesome as the infosuite.

No problem, you took the time to write it, it's really a gold mine for beginners on Steam :)

I know this comment is a little late, but here's my thoughts on this Duketown idea.

1. As it's been said, making a version of the map even remotely close to the original in terms of layout would be incredibly difficult, and even if you were to pull it off, it would look quite limited. (It wouldn't be so bad if we had TROR and polymer from eduke32 but we don't in megaton).

2. The gameplay is completely different. COD is all about slow movement, iron sights, sniper rifles, headshots etc. Duke is super fast-paced with relatively inaccurate guns blazing non-stop. If the map were to be made, I just don't think it would flow very well and people would only play it as a novelty.

I'm actually sort of working on a version of Sausage Factory for DM, and I can tell you that things which are extremely simple and standard in a 3D engine take a LOT of skill and elbow grease to pull off in 2.5D, if it's possible at all.