Anyone know why GoG doesn't have the linux version and steam does? I was going to get this from GoG but I guess I won't be able to :(

Edit: found the answer to my own question. From developer: "Because we use Steam or Galaxy for multiplayer a GOG Linux version would have to wait until GOG Galaxy comes for Linux."

That is rather sad really.
As a Windows user I didn't really take notice at the lack of Linux support.

Coming from the Hammerwatch devs I figured it would allow direct IP multiplayer, as Hammerwatch did and it looks like an extension on the same engine. When making my purchase yesterday I were actively trying to decide between Gog.com or Humble, in the end the DRM free option won out for me, guessing that if my friends picked it up on Steam I'd still be able to play with them cross-platform.

Oh well.
So far I've completed the first level. Nothing mind-blowing. Feels just as it's portrayed: A top-down serious sam running in something that looks like the Hammerwatch engine. Meaning more weapons, less playstyles from Hammerwatch.

You're not missing out on anything seriously amazing, at least as far as I've come so far if you decide to wait and see.