Populous the Beginning It's a unique game, very simple to learn and play and with more advanced spells, it's fun as heck to wreck havoc in the enemy tribes. Send a single well positioned priest with invisibility and magic shield and watch the enemy tribe fall apart while your priest convert dozens of enemies into your warriors.
Still haven't found other game that play like Populous 3. While there are plenty of RTS, having a Shaman(hero) and the individually comandable minions, together with the destructible/deformable enviroment makes it a unique experience and a landmark in history.
Hard to pick one of the huge list. Since it's one of my favorite games ever (since the time games had actual humour) and because many "high profile" will get much more recomendations, gets my vote :)
Pajama: EDIT: I see I've been beaten in recommending Dishonored which just goes to show what a good game it is :) but I'll add a recommendation for
King's Bounty: The Legend. Another excellent game (one of my favourites I go back to) that will keep you playing just one more turn. It's fun, highly entertaining and just so easy to get into. I'll definitely say give it a go :)
It's great but gets repetitive after a while. Enjoyed much more Armored Princess/Crossworlds than the Legend, maybe because of more varied units makes (and higher level units available sooner) the game somewhat less boring.
Dragons on the Legend are freaking OP and playing with a single stack makes the game too easy, even on impossible, as a mage.
Neither the less I have probably over 300 hours on both games, so can fully atest your recomendation.