At the risk of hooking you onto another game ... but the best fantasy, strategy, tactical turn based PC game imo is Age of wonders 3.
It's not free but not expensive imo but gameplay is really rewarding.
There's massive strategy as you can plan in advance what race, what Hero and what strategy you want to try out with them and it's highly tactical as well as you have to adapt to a lot of different opposing units.
As a reference : Ive been playing games for over 40 years and played tons of TBS games including the Civ series and that magnificent mod Wild Mana ( fantasy civ ) but :
when it comes to boardgaming, my nr1 pick is Mage Wars
when it comes to PC gaming : Age of wonders 3
here's the link anyway
http://ageofwonders.com/category/news/PS there's a similarity between MW and AoW3 : it can be overwhelming at first. Not that the gameplay is necessarily difficult because it's not but there are a lot of mechanics ,abilities, skills, to digest and there's happiness to monitor and diplomacy.
Just start up a random new game and checkout your hero and his starting unit's abilities and you'll know what I'm talking about. It gets easier with more play.
Just like you would start MW as a new player right now and you have all those unknown cards to digest ...
a challenge, but fun at the same time, right ?