I decided to give Heretic a go as well, since I never played it properly. It’s an interesting experience after Doom.
First of all, there are a lot of enemies. And I mean a lot. I think Civvie11 mentioned that in his retrospective, but a rare Doom map has over 100 enemies. In Heretic, every map has more than that. I don’t know if it’s an attempt to make the game harder/longer, or maybe they had more resources, or put those Tomes of Power to good use. But you get tired of killing all of them. What’s more, unlike Doom maps, that are quite “abstract”, Heretic maps have more of a “hub” design. That means all those monsters come at you at the same time, from different directions.
I didn’t notice previously that although you have inventory, not all items are persisted between levels. Seems like you can carry just one Tome of Power, and no Wings. Probably that was an attempt to balance the game.
Probably one of the biggest disappointments in the first episode is the fact that there are just 4 weapons available. Which is as boring as playing the entire first episode of Doom without a rocket launcher.
Interesting that the first episode of Doom put two Barons of Hell as the end bosses. And Heretic puts two Iron Liches. Speaking of which, the whirlwind attack that raises you is a neat trick. As well as the “explosive barrels” that can be moved on that level.