I'm considering getting this as I've been wanting to play the original RE games and I've heard there are some really good mods for the PC versions like Kendo's Cut for RE2, so has anyone tested if any of these mods work with this or did the GOG patches break compatibility?

Edit: Apparently the first game is compatible with a bit of additional patching but the other two likely won't be

Yeah, there's absolutely a reason Gemini chose sourcenext and not the original 90s ports. This is as bad as when Square rereleased the original awful pc ports of FF7-9 on pc and based all their modern console releases and the re8 remaster on them. They're AWFUL. GOG claiming these are the best versions of these games is a fucking joke.

Alright, thanks for the answer. I think I might grab this anyways to see the game as it originally was

I believe Classic REbirth works with RE1 but only if you install the Japanese version.

You can get it to work by installing the Japanese version.
Go to Mange Installation > Configure > Language > Change to the Japanese looking one > OK

Then you need to update the Biohazard.exe from the Classic Rebirth site.

Grab the Official 1.01 patch by CAPCOM and just drop that into the installation folder and overwrite the original exe.

That worked for me.

I recommend playing around with the config.ini that it generates after you run it once.

To confirm with josesuicidio, the Japanese version (which GOG provides with the English version) can be patched to work with the Classic Rebirth mod (as confirmed by PCGamingWiki: https://www.pcgamingwiki.com/wiki/Resident_Evil).

You should remove the "solution" tag from his post since he will simply confuse newcomers.

if you install the japanse version of the game you can install rebirthpatch

I don't see any option for doing so

Is the Japanese Version that GOG includes the original pc port or is it the sourcenext version?

There is no sourcenext version of the first game but I think they confirmed all three games will be the original versions

RE2 will be, no info about RE3 yet I think.

Yea, RE1 had MediaKite release, not Sourcenext.

One option for GOG and Capcom might be to provide unmodified CD/DVD images of MediaKite and SourceNext releases as bonus materials. In this way the versions needed for Classic REbirth patches would be legally available in the same package with the GOG releases.

CarcinogenSDA just posted a video on how to install the Rebirth mod

I'm going to make a presumption and say GOG probably know the REbirth mod is a thing (I say that considering the numerous re-releases of other games they've done in the past that include fan mods to fix things right out of the box) but either Capcom said "No" (they made their negative stance on mods clear last year) in terms of negotiating or they didn't get access to the SourceNext versions of 2/3, so they didn't bother going into discussions with the REbirth team.

Seeing that the JP version on GOG is compatible once you use the 1.01 exe, I'm going to hold some faint hope the SourceNext version quietly exists with whatever modified US version of 2/3 GOG are going to push if you use the JP language option for install. Either that, or if enough people complain, GOG will somehow negotiate with Capcom to get the SourceNext versions as an extra download (as they've also done this in the past with things like the Star Wars space simulators having unique versions ranging from DOS to the Windows version).