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I recently purchased this for myself and 2 of my friends here, and I came to realize that there is like 0 support and help from the community. There is 0 maps you can get online even though there is an editor in game to create maps. This version of this game has so few of the features the steam version has its really ridiculous to compare. I regret buying the game on GOG. I had no idea it would be so limited here.
Many people here are not too much into multiplayer and are fine with single player games. I hope this will change with Galaxy. I haven't tried multiplayer from GOG because there's no Linux version yet, but that's a thing for the developer. I have to agree this version has less content, but again this can be solved by the developer making all the things compatible with this version (and in the best scenario adding cross-play between Galaxy and Steam).

About the support, it can vary from one game to another. I can tell you that community support in the Heroes of Might & Magic forums is good. And in general GOG support is very good. So if the community can't help you, you should try to send a support ticket. If they can't help you, you can always ask for a refund.
and for me all works
Official maps are still not included in the GOG version. Unepic official site says they will be. Dev needs to copy paste. And yes, I own the steam version since posting this, and thats all it took to get the official maps to the GOG version.