Wads with easy progression like e1 and map 1-7 of doom 2?

[invictius]

These are rare nowadays. First map should only take a minute or two then gradually get longer. Few megawads follow iwad-like progression for the first several maps.

[Graf Zahl]

You don't need to look further than Deathless. 4 Doom 1 episodes roughly on par with the originals.