(PLEASE ENABLE WORD WRAP)

If you're honestly wondering if this mod will run with Brutal DOOM-- no, it won't. Not now, not ever.
Don't request BD compatibility, because it will never happen.

Also, ZX does not support deathmatch or alt-death. Co-op, however, is supported.

QSZX is a gameplay mod, and is an overall total replacement for everything but maps, so it likely won't work with anything that replaces weapons, armor, powerups or monsters without a patch. 
Unless you compile a fix yourself (and good luck, best wishes if you do- send it my way when you're done, 'cause I would play the hell outta that), playing QuakeStyle with something like KDiZD ain't gon' happen any time soon.
UZDoom's flexible but it's not a contortionist.
However, custom actors that DON'T replace a standard DOOM actor will probably work as long as they don't share a sprite or actor name, or they don't replace an actor that ZX also replaces.
Do be advised that some game mechanics, like melee-kill ammo drops, won't work with non-ZX monsters unless patched to do so.
Even then, they might not quite get along right should you be using the Bolognese-based gore mod.
Custom weapons are out on principle; all the mainline weapon spawners are replaced by ZX's RNG-based spawner behavior...and then there's the weapon wheel. 
Integration of a weapon into the mod is by no means impossible, just tedious; you'd have to implement it in all the player classes, requisite spawners *and* the weapon wheel.
Custom ACS scripting generally won't be affected, though there are hiccups here and there with older ACS, like DAEDALUS.WAD.
Very few, if any ZX actors have a DoomEdNum defined, so that shouldn't result in many conflicts either.
Note that Bolognese and Classy Bastards are 100% OPTIONAL. It'll work perfectly fine without 'em.
Savegames with an addon in place will break if that addon's not in place, and savegames without addons will break should an addon be present.

Known levelset/TC incompatibilities:
DAEDALUS.WAD- At two times in the first hub, a Hell Knight has to be killed to acquire a key to progress. Unfortunately, with changes in the mod and UZDoom, even if you luck out and get a Hell Knight, it won't drop the key. The keys can't be summoned or given via the console, either- this is old-world DECORATE and DeHackEd stuff. Like first-gen DECORATE- and unless you can contact an OG member of Team TNT and figure out what scripts to execute, the only fix is to make SZ_HellKnight replace the stock HellKnight actor. This comes at the cost of revenants, deathnaughts and Hell Warriors being unable to spawn, and I'm not willing to lose three enemy types just to make one levelset, even a good-if-confusing one, playable. A patch could make this work, though.
PSX DOOM TC- This TC modifies too many global variables, mostly gravity and the cast list, for ZX to work with it. Try the Consolation Prize version instead. Even then, some animated flats won't quite match up.
Doom 64: Retribution- See the PSX TC above. Consolation Prize is your friend here. Even then, it tends to goof on certain maps.
KDiZD- Graphical errors and unreplaced custom actors. Could be patchable, but unlikely to happen; I don't like the mapset too much.
Doom Gaiden- Unreplaced custom actors, and greatly differing gameplay styles.
Brutal Doom- No. Just...just no. QuakeStyle ZX is about enhanced gameplay, not a giant love letter to the DOOM comic book. In any event, conflicting custom actors are the order of the day. Don't expect a patch-- we've already got a Bolognese gore addon, OK?
Pirate Doom- Why would you want to play Pirate DOOM with ZX's weapons? ... In any event, there are graphical incompatibilities that ruin the atmosphere, alongside some weapons not being replaced.
Ancient Aliens- It runs, but looks farkin' terrible because ZX and AAliens have wildly different color palettes. I might be able to make them work together eventually, but it would take a lot of work, redoing all the sprites as PNGs. Quite a few actors are dependent on pallette translations, and changing the mod to be otherwise would add a not-insignificant amount of file size.
Back to Saturn X- There are unpatched ANIMDEFS in BTSX that don't jive with ZX as it sits. Plus, the color palettes do *not* line up.
Evilternity- Custom actors out the wazoo that don't jive with ZX at all.
Doom Tribute Project- The scripting and custom weapons don't get along with ZX. I might make a patch eventually.
SIGIL- not incompatible, really-- it runs and it's playable-- but there are certain times you need a hitscan weapon to advance in the levels, and certain loadouts don't have them-- so you'll have to target the evil-eye decorations, drop down the console and type "MDK" to fire a hitscan tracer at it to open the way forward. Do keep in mind that MDK is a cheat command-- short for "murder death kill"-- it's designed to instantly kill most any monster it hits, so use with care.
Purgatory- incompatible by choice. I could patch this to work, but I don't want to. Fuck this mapset.

Here's what the addon files do:
qszx-bgore.pk3- a version of SGT MarkIV's Bolognese gore mod custom-tooled for ZX. OPTIONAL.
qszx-cb.wad- "Classy Bastards". OPTIONAL. Offers a variety of loadouts to start one's game with, most of which come with a unique starting weapon. You might get the Debug Guy class if you know where to look, cheaters... :-P

Here's what's in tbe "patches" folder:
QSZX_D64D2_chaingunners.wad- A patch for all known versions of D64D2 that has chaingunners subbed in for nightmare imps.
qszx-njzd2001.wad- a little patch for the Enjay ZDOOM 2001 levelset.
qszx-Thunderpeak.wad- a patch for the Thunder Peak one-map wad.

Here's what's in the "accessibility" folder:
qszx-noscopetint.wad- an accessibility patch that removes the colored tints from all the scope graphics.
qszx-nocolortags.wad- an accessibility patch that removes all the color-coding from the weapon and item tags.

And here's what's in the "docs" folder. Don't remove any of these files:
qstylezx.txt- the information and credits file.
readme.txt- this file.
armor.xls- an Excel spreadsheet detailing how the Guncaster-inspired armor system works. Designed to be viewable in Google Docs, OpenOffice, LibreOffice, etc.
Changes.txt- the detailed changelog since the last public release of the mod
DAMNUMS Info.txt- the copyright notice and information relating to Xaser and Major Cooke's "DAMNUMS" mod that's integrated into ZX.
classybastards.txt- details on the Classy Bastards addon (qszx-cb.wad) loadouts

On the IWAD front, it's only meant for DOOM (registered/Ultimate), DOOM 2, Final DOOM (that's TNT and Plutonia), SIGIL, the Master Levels and NERVE.WAD ("No Rest for the Living"), as well as most WadSmoosh packages.
It'll probably work with FreeDoom, but the graphics are gonna be all over the place. I'd stick to the original IWADs or a version of FreeDoom that's been stripped back to the levels, textures, music and flats...overall, PWAD-ified.
I'm not sure if it works with the BFG Edition IWADs; more than likely it does.
If you can't find somewhere to buy 'em (not likely, as there's Steam, and the game's cheap as shit), can't afford 'em or are just too damn lazy or cheap to fork over the cash, get 'em off of an abandonware site or the Pirate Bay. 
Trust me, they're out there somewhere.

Oh, one last note: should you play D64D2 with this mod, you might want to go easy on stealth. At some points, the levelset relies on you alerting the monsters with gunfire to trigger the level scripting.
-Xterra

Now just for the hell of it, here are some of my favorite other mods, because play them too:
*Ratchet and Clank: Hot and Bothered by Vermilion Rua (FKA Scarlet Mango): "Thanks for the armories!" Authentic, lovingly-recreated Ratchet and Clank action against the forces of Hell.
*QuakeStyle Neo by BathySalts: A brilliant multiplayer fork of this very mod series. It's amazingly executed, and makes me proud as hell.
*ROverkill by Pillowblaster: This needs no description. Just go get the damn mod already-- but support Ukraine instead.
*Samsara by TerminusEst13 (later maintained by Kinsie): Think "Generations Arena" for DOOM, and add in some guest fighters. Like Duke Nukem. And the Marathon guy. Yeah.
*Samsara Reincarnation: Samsara, but more. LOTS more. Is good.
*Demonsteele by TerminusEst13: From Samsara's creator. Weeb DOOM. YATTA! Jokes aside, it's very very fun, action-packed and visually pretty. If you want a little anime in your DOOM, go for it.
*Pirate DOOM: Yo ho ho an' a bottle a' Jack. Hilarious, very well-designed and fun, with a bit of Monkey Island flavor. Plus, at one point it plays "Highway to Hell".
*The Golden Souls and Golden Souls 2 by Batandy: Mix Mario with DOOM and you get these masterpieces. One downside to both that for all the effort that went into the levels, the weapons suffered a bit and require work. My advice? Get a lump editor, learn DECORATE, and tweak 'em like I did! Though be ready for frustrating levels.
*QuakeStyle, DoomZone, ZAGE and Doom Gaiden by SilentZorah: Now how could I go without mentioning SZ's other work? Seriously! Go play 'em. Be prepared for a challenge, though- he makes his mods harder than mine.
*Project MSX: Doom with a side of Crysis, FEAR, Halo and Metroid Prime. Very fast-paced and thrill-a-minute.
*REELism and REELism 2 by Kinsie and 100 Pounds: Fun, variety-laden survival mod with a hearty helping of biting, sarcastic humor. Pretty much Kinsie in a nutshell. Might want to avoid this if you're a brony/CoD fanboi/dudebro/*insert fandom here* who can't take a joke.
*NAZIS! by WildWeasel: WolfenDOOM taken all the way. Invoking Godwin's Law was never so fun. For extra flavor, try combining this with one of Laz Rojas' old WolfenDOOM TCs.
*DOOMRL Arsenal/Monsters by Yholl, Sgt. Shivers and co.: DOOM with an RPG-style twist and some really, REALLY cool new weapons and monsters. Takes heavy inspiration from Kornel Kisielewicz's Doom roguelike.
*Zero Tolerance for Zero Intelligence by Zero Prophet and Xaser: If Zharky_X was dead serious and not actually disturbingly dark comedy all along.
*MetaDoom by Kinsie: Amalgamation was never so fun.
*Metroid Dreadnought by TerminusEst13: Doomtroid Prime. Absolutely fantastic.
*Guncaster by Pillowblaster: Dragons. Guns. Magic. Power armor. Dragonforce. Tom Jones. This mod's got it all.
*Trailblazer by Pillowblaster: "Ain't over 'til it's over / Ain't over 'til it's over!" Channel your inner Dirty Harry and go crazy.
*DOOM 4 DOOM by DBThanatos et al.: Take elements of new DOOM, fuse 'em with old DOOM. FYP2016 FTW.
*Final Doomer by Sgt. Shivers and Yholl: Thematic weapons for thematic levels. They all play and look great.