So, I owned this game on steam for more than five years. The GOG version is compatible with TModloader, the official unofficial mod framework, but it is very hard to install mods as usually they're put in Steam Workshop. I really with GOG can have a negotiation with Terraria modders and somehow making modding GOG version easier. However, unlike Minecraft, the stock (vanilla) feeling of Terraria is still extremely polished. 5/5. It is a really casual game and GOG, with its online installer, makes it truly portable and can be played in some secondary schools that block Steam.