I missed this game so badly, is there any free version downloadable out there somewhere?

www.gog.com or Origin got sell..

or try War for the Overworld on Steam : http://store.steampowered.com/app/230190/ (the spiritual successor)

free version you'll need to dig around the internet for it..

War for the overworld seems exactly or very similar like DK, is it almost the same? Which one is better in terms of gameplay experience?

Game play and mechanics very similar. They trying to be as close as DK2 but not to be an exact clone.
Names of minions are different but its more or less the same thing with a lot better graphics.

But do note, this game is still quite buggy. The devs are constantly fixing and improving it, but still has weird quirks from time to time. Still a playable game tho. Worth a try but better buy during a steam sale.

I think you missed origin in the house.

Dun forget about Dungeons 2: http://store.steampowered.com/app/262280/

This and Overworld are following DK2 footsteps but.... read the reviews for their flaws.