You'd never think it was possible, but I've gotten very emotionally attached to this short, dozen pack mapset. As such, this is going to be a somewhat personal review. Apologies in advance.
Altars of Madness' approach to Doom is to focus squarely on compact combat puzzles with calculated geometry. As such, it is pretty clearly inspired by the work of Ribbiks. It also forces pistol starts each map. Its brevity, conciseness, and general gameplay loop make it ideal for new Doom players looking to hone their skills.
For me, I took much longer to beat these twelve short maps than you might think. That's because I didn't play Altars of Madness with the intention of pushing through to the end. Somehow, one way or another, Altars of Madness became my guidepost. Something I would check in on every now and then while I played other Doom WADs. When I started playing this mapset, I struggled. A lot. The forced pistol starts and dense combat seemed like they would be too much for me. But as I played other Doom WADs and circled back to this one, I found the maps getting easier. Yes, in a weird way, because of my awkward way of playing this game, the difficulty curve was almost inverted.
I have since played quite a lot of Doom, and I've wildly fallen in love with some blockbuster megawads. Altars of Madness certainly isn't as good as those, but it's special to me. I'm going to miss this mapset's watchful eye observing and rewarding my improvement.
Cheers to you, Alex Decker. For this mapset and your good taste in music.