

I've been working on a content expansion for Heretic (monsters, artifacts, etc.), as well as a moderate rebalance of the gameplay. Gameplay-wise, I think the biggest problems with Heretic are the weakness of many of the weapons and the fact that most of the monsters are very similar to each other. Heretic's relative lack of textures does suck, though it isn't a problem unless you really want to use vanilla Heretic, which I would agree is not very viable for modding. On a related note, vanilla Heretic may have fewer linedef actions than Doom 2, but it also has more sector types, including the scrolling/pushing floors that allow for a huge amount of Boom-like pseudo-scripting. The latter should also allow you to use fast doors, or at least something functionally identical. In vanilla Heretic format you can use the voodoo dolls, and in ZDoom's Heretic in Hexen format you can use the scripting. I'm having a hard time finding more specific information, but I think locked switches were made possible in Boom through the use of voodoo dolls, and in ZDoom formats through the use of scripting.
FLYING DEMON HERETIC GAME CODE
Vanilla Heretic doesn't have the fast door actions introduced in Doom 2 (because its code is derived from Doom 1), but I believe none of the vanilla Doom engine games (except maybe Strife?) have locked switches. So is there anything else you can think of? No "expansion pack" with new monsters, weapons, textures and music like Doom2 was for Doom. Heretic has only about a half to choose from (if I do not count different kinds of same monsters like scratching/firing gargoyle, non-shooting/shooting golem and the shadow variants etc.) Doom has overally the highest amount of monster types among many games that existed that time, and each monster is unique in some way.

I personally think that they should have made something like D'Sparil's staff (at lease for the two expansion episodes) with similar destructive effect as BFG.

Heretic has 7 weapons (same as Doom) and they almost match each other between Doom and Heretic. Doom has really rich palette of switch types. A regular switch and exit switch (which is often used for a regular switch in custom maps). Even if these were not used in original levels, they should have left them available in source code to be used in custom levels. Most importantly fast opening/closing doors, switches requiring a key etc. Lack of many linedef actions which were present in Doom. So I'm trying to come up with list of things which Doom did better and what I consider being the biggest flaws of Heretic: Nowadays I play Doom much more (but still return to Heretic sometimes) and I started realizing that even through Doom was older and technically a bit less advanced (engine-wise), it did many things better than Heretic. Especially during my childhood I preferred Heretic over Doom as I was more familiar with its medeival theme, and loved the weapons and everything. Heretic was the next game based on Doom engine, and it definitely brought some important engine improvements (looking up and down, flying) as well as gameplay and graphical experience (fantasy weapons, monsters, Tome of Power) and excellent soundtrack.
