Napalm A single map for TNT:Evilution (that is, run it with -iwad tnt) by the author of Generator of Evil and Remain1. It's a bit messy, for instance it uses too many different texture themes (but I'm not so sure that's not just a symptom of its underlying IWAD - TNT is also rather messy) It's not too hard if you're careful but you will have to explore; progression is only made via routes which in other wads might be considered secret areas. That said it has some clever tricks, like a fireable cannon, lots of actual secrets, and plenty of windows and future glimpses to draw you into playing it all the way through. Pretty good and worth playing, I think.
E1 The Test When I saw the 80 shells in the first room I thought this one is going to be easy. Far from it. It took 3 attempts and in the end I ran for the exit without killing all the monsters. It's a small techbase which replaces E1M1, but doesn't have much in common with episode 1, just being made up of three entirely unconnected branches. It's very frustrating because you think it should be easy but it's just slightly too cramped. Apparently inspired Doom Incarnate, which is much better.
Lemmings Doom This is a partial graphics conversion, some of the monsters and weapons are replaced. It's not bad, the lemmings seem rather large, but they're the size of Doom monsters so what do you expect. There are also sound replacements, all lifted directly from the game, so they all sounded insanely familiar to me (especially the ones I used in records) It works with any IWAD but mostly replaces Doom stuff rather than Doom 2.
Dead Zone All 9 levels of episode 2 are replaced. It's all a bit simple and mid-90s-esque, not that that's a problem, but the gameplay is rather lacklustre. I actually got bored of shooting the monsters, which seem to be in big groups of the same type, which queue up to be slowly ploughed through. The light level doesn't help either, the author doesn't do himself any favours using mass lights-off effects*. Having said all that E2M3 is pretty interesting for speedrunning purposes and E2M7 would be good if it weren't for the aforementioned lighting.
* He doesn't do himself any favours using DoomCAD either, and I think that's the real problem - DoomCAD is one of the few map editors I've actually used, and, well, put it like this - it makes Yadex look good! It certainly explains the lack of variety in monster placement, as I definitely recall DoomCAD being a right arse when you want to change the type of thing being placed - it lends itself naturally to placing lots of the same.