The GOG version has zero, advantages over the free Steam version. The executables and game data are identical and the additional expansions on GOG are available for free, legally anyway.

Step 1) Download Shadow Warrior Classic for free on Steam.
Step 2) Download the two expansions(one of them is available on the 3D Realms website for example) to your Shadow Warrior directory.
Step 3)Now your Shadow Warrior install is identical to the GOG one.

That's truly unfortunate , i guess someone asked them the same question and got this reply
https://twitter.com/_ShadowWarrior/status/339856261703151619

That guy is a complete moron... He was bitching because he "lost" 6 bucks... I played the game when it was re-released and I don´t regret it. Great time.

Is the requirements section screwed up? It says the game is still running under DOSBox. And it requires 2GB of hard drive space? Yet the Mac requirement says 600MB. What the hell?

To be honest, it just looks like the game is running at a higher resolution.

There was a team that was trying to restore the lost third expansion pack, but now it looks like they're going to Devolver Digital. I hope this doesn't mean a Steam exclusive release for that pack. :(
https://twitter.com/devolverdigital/status/355170624823496705
Edit: Or rather, digging a little deeper, it seems the original producers had been essentially sitting on the release for some time now. It's just given the timing with the Classic Redux pack, I'm worried that they will ignore the GOG version.

Lets hope they don't ignore the GOG version. I still feel burned about the Duke Expansions.

The "redux" version is lovely, just got it today on Steam for $3.

This is how I like to play these games... they look and play as close to the originals as possible but still have a crisper look and modern controls. It's really lovely. The Duke 3D version on Steam is equally nice.

I wish GOG got these versions.

Why? Would you buy them again, or something?

I would have rather had them here. That's why I waited for the sale price.

ya i got em as well , im loving it haha fills up the screen nicely plays well have no issues

They should simply call this "no more tears shadow warrior edition"

just waiting for blood redux and multiplayer / co op for shadow warrior and duke nukem

This title and Duke Nukem Megaton edition also have linux versions available as public betas, for those interested. They're also offered as a heavily discounted package for a limited time period.

Not only that, but Duke also contains the expansions that are not in the GOG version at all, as well as the original game without atomic. That's just one cool package.