Steam release mentions these features for the steam edition:
Fully remastered to work with modern systems
Insect Invasion, Mod SDK (C++) and all patches included
Re-implemented multiplayer and NAT traversal for a smooth online experience

Just wondering if GOG version is the same or just a release of the original game?

Just wanted to say that response time was really pro. Niiiice.

Thanks for the info. Would it be possible to get the IC page to state somewhere that Patch1.1, 15 expansion creatures and Insect Invasion are included please?

insect invasion is not included in either version. that is only available for the disc version.

I'm quite certain the II is preinstalled with the game in this packaged version; you just select it from the main menu.

Stop spreading misinformation.

I was wondering about this question too and yes if you would look in the folder where impossible creatures is installed you’ll see the SDK, insect mod etc.

To clarify that insect mod is just that and you select it from the button for mods. It will not appear in the campaign, just gives you insects that you can use in the army builder to create custom armies to use in player VS computer/multiplayer.

As you probably all know by now if playing the game for any length of time, the army builder is available in game with the campaign but for other game modes you build your armies save them and they appear in the custom armies list when you set up your teams in the other game modes outside of the campaign.

To switch back you have to return to the mod section and then select IC from the list of mods to go back to the unmodded game in order to play the campaign.

If you move to another computer, to transfer the newly created armies that you may have done go to the profiles folder ( located in the main folder ) look in there and new armies for the main game will be found multiplayer folder whereas created armies for each particular mod will be found in their own folder such as “Insect .“ To be thorough just copy the whole profile folder over to the new install of Impossible Creatures

The one advantage I can see with the Steam version is the Intergated workshop and the availability of Mods through that .