For the people who bought the GoG version of Kingdoms:

Does it include the post-release extra units like the Riktus, Mer Warrior, Rolling Tower, etc?

Far as I know the post-release units were units packaged with the Iron Plague expansion - however that got a very limited retail release and many people could not get hold of it. The post-release unites were later given away for free for the 4 existing races mostly for those people that could not get the expansion. They never however released the 5th army for free (that remained with the expansion alone).

So yes you do get the post release units - and the 5th army and the campaign :)

Ah okay. Yeah, I saw that it came with Iron Plague, but didn't know that the extra units were in the expansion. I first got the original game when it was in the bargin bin a few years after it came out and downloaded the extra units on their website before I ended up finding the expansion, so I ended up having the extra units before I actually had the expansion.