With NeoGeo emulation being what it is, I thought it would be best to populate a list of which games are using DotEmu or Code Mystic emulation. A few DotEmu NeoGeo releases have been updated silently a while back, using Code Mystic emulation instead. This has gone officially unmentioned by GOG and SNK with some users mentioning it in a few threads as well as reviews.

The general consensus is that DotEmu releases are best avoided due to piss poor emulation with the only workaround being to use an outside emulator with the included romsets. The following link below will help with that aspect, otherwise purchasing any of the DotEmu versions is best avoided.

https://www.gog.com/forum/general/roms_obtainable_on_gog_compendium

Please keep in mind that I can only check and confirm what games I happen to own. If you have anything that I am missing that can be confirmed, then please leave a post and I will update it later.

DotEmu:

ART OF FIGHTING 2
BASEBALL STARS 2
BLAZING STAR
FATAL FURY SPECIAL
IRONCLAD
THE KING OF FIGHTERS 2000
THE KING OF FIGHTERS 2002
KING OF THE MONSTERS
THE LAST BLADE
METAL SLUG
METAL SLUG 2
METAL SLUG 3
METAL SLUG X
NEO TURF MASTERS (no longer available for purchase on GOG)
PULSTAR
REAL BOUT FATAL FURY 2: THE NEWCOMERS
SAMURAI SHODOWN II
SENGOKU 3
SHOCK TROOPERS
SHOCK TROOPERS: 2ND SQUAD
TWINKLE STAR SPRITES

Code Mystics:

3 COUNT BOUT
ALPHA MISSION II
ART OF FIGHTING 3: THE PATH OF THE WARRIOR
CROSSED SWORDS
GAROU: MARK OF THE WOLVES (silently updated to Code Mystics from DotEmu)
GHOST PILOTS
THE KING OF FIGHTERS '97 (GLOBAL MATCH)
THE KING OF FIGHTERS '98 ULTIMATE MATCH FINAL EDITION (2018 version with no rollback update)
THE KING OF FIGHTERS 2002 UNLIMITED MATCH (2018 version with no rollback update)
THE KING OF FIGHTERS 2003
KING OF THE MONSTERS 2: THE NEXT THING
KIZUNA ENCOUNTER: SUPER TAG BATTLE
THE LAST BLADE 2 (silently updated to Code Mystics from DotEmu)
LAST RESORT
MAGICIAN LORD
METAL SLUG 4
MUTATION NATION
NINJA COMMANDO
NINJA MASTER'S: HAOH NINPO CHO
OVER TOP
ROBO ARMY
SAMURAI SHODOWN IV: AMAKUSA’S REVENGE
SAMURAI SHODOWN V SPECIAL (silently updated to Code Mystics from DotEmu)
SENGOKU
SENGOKU 2
SOCCER BRAWL
SUPER SIDEKICKS
THE SUPER SPY
TOP HUNTER: RODDY & CATHY

Since you own Magician Lord and Metal Slug 4, could you please tell me if those games include the original rom?

I do see your list above, but am merely curious: Do you own either GOG release of Samsho 4 or Kizuna Encounter? Are they definitively Code Mystics releases?

Here are some additions to your list (bolded titles under DotEmu are additions to your list). PCGW indicates the dev on each individual game's page - the majority of games which are DotEmu releases are also featured on Humble Bundle.

DotEmu:

ART OF FIGHTING 2
BASEBALL STARS 2
BLAZING STAR
FATAL FURY SPECIAL
IRONCLAD
THE KING OF FIGHTERS 2000
THE KING OF FIGHTERS 2002
KING OF THE MONSTERS
THE LAST BLADE
METAL SLUG
METAL SLUG 2
METAL SLUG 3
METAL SLUG X
NEO TURF MASTERS (no longer available for purchase on GOG)
PULSTAR
REAL BOUT FATAL FURY 2: THE NEWCOMERS
SAMURAI SHODOWN II
SENGOKU 3
SHOCK TROOPERS
SHOCK TROOPERS: 2ND SQUAD
TWINKLE STAR SPRITES

Code Mystics:

THE KING OF FIGHTERS '98 ULTIMATE MATCH FINAL EDITION (2018 version with no rollback update)
THE KING OF FIGHTERS 2002 UNLIMITED MATCH (2018 version with no rollback update)
SAMURAI SHODOWN V SPECIAL

I was astonished when I saw Ninja Master's and Kizuna Encounter. two of their most underrated jewels, but do these new re-releases have online capabilities like the previous Code Mystics works? If they don't, then i'ts rather disappointing.
Speaking of disappointments, the old, nasty DotEmu farts like that Last Blade 1 emulation with choppy framerate and their absolutely useless repackage of Real Bout 2 with non-configurable controls haven´t been updated. Such gems deserve some love.

Although this does not answer your question, Samurai Shodown 4 by Code Mystics does not have multiplayer. It also does not have offline training mode.

Thank you very much, I think it's safe to assume that's going to be the case with this whole set of releases, and given the file sizes I don't even expect unockable concept art either. Truth is I had taken training modes for granted as they already added them to most of the catalogue back in the days of PS2 re-releases, I'm still baffled by how lazy and careless they have become; not only that but by selling these games like that they have spoiled the appeal the CM brand had adquired with their releases up until now. It's sad they see this as just a chance for free money with no work put into it (even dropping work that had been done in the early 00s already!). "At least it's not a DotEmu job" doesn't cut it anymore, CM themselves had raised the standard already: I won't be buying them.

I bought Magician Lord and Overtop and was able to extract the roms, but I had to use a modified python script for the last blade 2 which is located here: https://misterfpga.org/viewtopic.php?t=1423

The roms of course are located under the Data folder in the Game directory.

I had to change the code to look something like this:
#!/usr/bin/env python3
# SPDX-License-Identifier: CC0-1.0
from pathlib import Path
import shutil

from convert import config
from convert.tools import split
from convert.graphics import pixel_cm4_to_ng4
from convert.mapped import InterleavedFiles, SequentialFiles


def maglord(outdir):
maglord = outdir / 'maglord'
maglord.mkdir(exist_ok=True)

with open('p1.bin', 'rb') as i:
maincpu_parts = [
(maglord / '005-p1.p1', 0x8_0000),
]
split(i, maincpu_parts)

sfix_source = Path('s2.bin')
sfix = maglord / '243-s1.s1'
shutil.copyfile(sfix_source, sfix)

with open('v1.bin', 'rb') as i:
ymsnd_parts = [
(maglord / '005-v11.v11', 0x8_0000),
(maglord / '005-v21.v21', 0x8_0000),
(maglord / '005-v22.v22', 0x8_0000),
]
split(i, ymsnd_parts)

bios_audio_source = Path('m1.bin')
bios_audio = maglord / '005-m1.m1'
shutil.copyfile(bios_audio_source, bios_audio)

with open('c1.bin', 'rb') as i:
files = [
SequentialFiles([maglord / '005-c1.c1', maglord / '005-c3.c3',
maglord / '005-c5.c5'],
[0x8_0000, 0x8_0000, 0x8_0000], 'wb'),
SequentialFiles([maglord / '005-c2.c2', maglord / '005-c4.c4',
maglord / '005-c6.c6'],
[0x8_0000, 0x8_0000, 0x8_0000], 'wb')
]
with InterleavedFiles(files, 1, 'wb') as o:
pixel_cm4_to_ng4(i, o)


def neogeo(outdir):
neogeo = outdir / 'neogeo'
neogeo.mkdir(exist_ok=True)

japan_j3_source = Path('sp_4j.bin')
japan_j3 = neogeo / 'japan-j3.bin'
shutil.copyfile(japan_j3_source, japan_j3)


def maglord_convert():
outdir = Path('mame')
outdir.mkdir(exist_ok=True)

maglord(outdir)
if config["partial"]:
neogeo(outdir)


if __name__ == '__main__':
maglord_convert()

Do the new Code Mystics ports have save states or any other quality of life options?
Would anyone care to comment on the input lag?

As far as Magician Lord and Metal Slug 4 go, there are no save state options.
They are lacking achievements as well.

That being said, the lag for myself has been unnoticable.
And from the start in the main menu with all the sound, video, and controller/keyboard customizing, you get the impression that these releases have had some care given to them.
Aside from a strange MS4 bug where I could not continue, I have had zero regrets with these purchases and am lookiing forward to more from Code Mystics.

I'm also very curious as to lag input experience from others, as I felt it to be as snappy as MAME emulation, yet I have no recent experience with physical hardware.

I appreciate the reply! Mostly good news, but no save state (or even a stage select?) is a bit disappointing.

I have the Hamster releases on PS4, which are great ports, probably the best out there. They have only one save state, but at least it's there.