ZDoom

/idgames link

It's The Ultimate Doom... But smaller. Four one-map episodes await. Each map is made in about 6-7 hours in an attempt at speed mapping that clashed with my ambitions. All difficulties are implemented on the finished maps. For added flavour, each map uses a different format. E1 is Boom, E2 is ZDoom (Doom format), E3 is ZDoom (HeXen format) and E4 is GZDoom (UDMF).

The maps are, essentially, old-school maps inspired by their respective episodes that use some added features based on format and convenience. Here's a screenshot from each map as-is (no prizes for guessing which is which):

Just bumping to say this is now released!

You can play E1 in any source port, I think, but you'll need ZDoom for E2 and E3 and you'll need GZDoom (with 3D acceleration) for E4 because of an experimental Hall of Mirrors room. I'm keen to see how people's computers handle that, by the way, as mine seems to slow momentarily upon first seeing it, but then smooths out. As it's pretty powerful, it may be that this rooms needs reconsidering or changing entirely.

so... is this like DoomOne where its all the levels connected as one big map, just with all four episodes?

No, they're just four maps I made, each themed after the episode they replace.