1. The Doom engine is arguably a work of art. Not for the faint of heart, surely, but well done, very well optimized and carries a simplicity that only a few of us (ie John Carmack) can achieve.

2. It was also open sourced a very long time ago by id software, which enabled a lot of tweaking by the community, and, therefore, a lot of knowledge.

3. Doom is a very famous game, having made a lot of success during it days. Everyone with even the smallest interest in games or computers that was alive back then probably played it.

4. Both Wolfenstein and Quake are also open source but the former is too simple when compared to Doom and Quake is too complex. As others have stated, Doom has 2.5D maps whereas Quake have full fledged, 3D maps.

All of this together surely makes it a good candidate for this type of experiment

When you say 2.5D do you mean that the map appears 3D but the player moves on a 2D plane?

Generating the layout of a map for DOOM is easy since the maps are essentially just 2-D structures composed of convex polygons with variable heights thrown in at the polygon level (aka sector). I'd imagine everything but the 2D geometry of the scanned area is randomly generated (textures, item and monster placement, heights of sectors, light levels, etc).

It has been open source for a long time and many great write ups and explorations of said source have been available.

It is known to be high quality and hackable, by orignal design and later hard work of fans.

By far the best write up is Fabien Sanglard’s Doom Game Engine Black Book [1]. The amount of detail and depth is just incredible.

[1] http://fabiensanglard.net/gebbdoom/

Try it. It's so much fun even today.

Seconded! I recently went back to the vanilla game and am playing through it trying to get 100% completion. It's very well designed and well balanced as well. Whenever I find myself low on health or ammo, there's usually a fresh box right around the corner, with plenty of secret areas to discover that are creatively hidden. Above all, it's just plain fun!

It's 2.5D and much smaller than average 3D games. The original game requires 4MB of RAM and a 386 processor, which these days is outclassed by microcontrollers.