What an addictive game! I wasn't expecting much, to be honest, but I installed it, played a bit, and here we are, 25 hours later. Yes, 25 hours for a single playthrough. Okay, yeah, I started over a few times early on, but once I got the hang of it I just kept going. The primary gameplay is match 3, with a slider rather than a swap mechanism. Each kingdom you conquer opens up a tavern and a ruin where you can find new relics, spells and items, and recruit new troops. To do this, you use some of the gold you've gotten in your warmongering, and then play a minigame. Higher level items and troops have a higher gold cost and a tougher minigame to play.
You can customize your newly acquired kingdoms with your chosen hero(s), troops, and relics, and use them in battles against kingdoms that you haven't conquered yet. You can outfit your hero with the items and spells you've gotten. All of these items have a color value and a points value, and each kingdom has either discounts or increased costs for using these items. (Ie, a kingdom might have lower point cost for blue and red items and troops, and higher point cost for red and yellow items and troops. Your hero's total cost is affected by his color and the combination of items and spells he or she has assigned.)
It's relaxing, but it can also be challenging, especially if you have trouble with the recruitment minigames.