...levels will basically consist of standing in a position, making some noise, killing the waves of curious monsters, go somewhere else and repeat it until all is cleared.
Now at least you have to clear out room per room, like Doom is supposed to be played.
I'm not sure what Doom you played, but I certainly remember using the fact that monsters will approach after you've shot your weapon (ie, the noise factor), then waiting at the side of the wall for them to come. This was almost mandatory in early levels when you lacked the big guns and/or ammo and the number of enemies were too great to handle simultaneously (particularly tons of formers with their insta-hits). The fact that you didn't have to do it often was due to either most enemies tracking you regardless or most projectiles were easily dodged.
Though, in spite of that, you do have a point. I'd rather not turn levels into a grind of luring and killing in neat lines. This, I imagine, is fixable via proper balance: only the noisiest sources would really make enemies come a good distance from their original location, like explosions and BFG blasts. Ranking the projectile weapons, I'd go: pistol, chaingun, combat shotgun, plasma rifle, shotgun, double shotgun, rocket launcher (explosion only). This is rough, but the pistol may have as little a radius as 3-4 tiles, and the loudness can go from there.
As potentially exploitable as it sounds, it's less of an exploit than the "enemies tends toward the center" that happens without a noise factor. Even if the AI for that is unchanged, I imagine there will end up a very little chance of it ever becoming useful when enemies are constantly responding to weapon fire and the dying breaths of their brethren. That noise could affect enemies would actually allow for the AI programming to stay near their spawning locations, rather than seeking an enemy they can't see or hear.
Rather than simply reacting to ONLY the most recent noise, I think there should be a rank in importance of noises for each creature....Basically, the higher the threat the noise is, the more likely the monster is to check it out. Choosing between a barrel moving noise and a BFG noise? Guess what I'd choose to concentrate on.
In fact, I'd even say that there could be a buffer with each and every noise heard recently for each creature. Hear me out on this: You hear a pistol shot (+X importance), you head towards it. For every step, the importance to you drops (to zero) until you decide that whatever did it would have moved on already (item is removed from the buffer). Then you hear a shotgun blast (+Y importance), and while heading towards it you hear a pistol shot (+X importance). Each creature type may have a different decay of importance for each sound (and I can see some mods really working with this) so you might follow the shotgun sound, but eventually that nagging pistol shot you heard earlier could be a lot more important.
Perhaps a better reason for the buffer idea is this: Hearing that shotgun blast might not be terribly important since you're investigating someone with a rocket launcher, but when you get to around where you heard the rocket explode you're going to want to check out the shotgun's sound since the rocket is a dead end.
We could break it down even further: Some enemies are stupid. No buffer. Simply check the importance of a new noise event against the importance of the noise being investigated. If it's higher - that's what we check. If it's lower, we ignore it. Some enemies are smart - they get a buffer system. Baron's of Hell and ArchViles just got that much meaner. My target dissapeared!?! Why YES I did hear something like someone teleporting nearby me. Let's check it out!
The buffer sounds like a great idea. I would, however, categorize most monsters in the "stupid" category, leaving (potentially) Barons/HKs, Arch-Viles, and formers as the intelligentsia. Of these, I'd rank Viles as smartest, then Barons, commandos, HKs, then the other formers (probably captain/sergeant/human, if they aren't all equal). It leaves some actual tactical differences aside from their somewhat predictable pathings. We could, in fact, go as far as to say that intelligent monsters can lead stupid but follower-type monsters (demons and lost souls come to mind, and imps specifically would follow HKs and Barons).
Mind you, if the enemy actually spots you, all of this additional noise pathing goes out the window and they follow their typical AI. The biggest difference in an actual battle is that you'll notice more monsters showing up in the middle, rather than being able to lure one enemy at a time (which is the case sometimes). This is why I don't consider it inherently exploitable, because in the end this is just a way for monsters to be more aggressive (creating the double possibilities for abuse on both parties).
Level's acoustic level. While in the cave you can precisely hear from where sound is coming, in the maze in could be definitely problematic. Acoustic level could be a complicated calculation that depends from the placement of walls and open space size, or dependent from the level type. If it's big then you can't precisely find the source of the sound, resulting in big variety of places to search (maze level). If it's low, you can almost "see" the location of the sound (caves or hell city).
Acoustics of a particular area are a nice little nuance that I'd love to see. It makes caves and arenas more deadly, but also somewhat easier (given you have some decent cover). Arenas, for instance, tend to contain a number of barrels, any of which can easily create a noisy diversion while you run away from it.