Rise: Battle Lines [Steam store page]
Bare-bones little game using the strategy elements you see in many hex turn-based games as almost a single-player puzzle. This part is short though, a couple hours, and probably just meant as training for the multiplayer component.

It's lacking any story, art, or variation that usually elevates this sort of single-player experience beyond rock-paper-scissors combat, and unfortunately the multiplayer doesn't have a useful number of players, so you'll have to bring your own friends if you want to try it.

A great combination of music, nice visuals, and a unique style of light strategy. Easy enough for casual players, with Bastion type difficulty settings.

Guild of Dungeoneering [Steam store page]
Some of the mechanics are unconventional, but once you learn how to play it properly it's a fun and well balanced dungeon crawler with a twist. It's one of the only rogue-like dungeon crawlers that I actually go back and replay from time to time.

Costume Quest 2 [Steam store page]
Better environments than CQ1, with the same great characters. The first level is the only bad part, so suffering through that small grind is worth it.

A survival card game with an interesting concept, but the flawed mechanics make winning more luck than skill-based.

Frozen Synapse [Steam store page]
A challenging turn-based squad tactics game, though sometimes the previews are completely wrong. Sadly, game invites pop up even when you're marked unavailable or playing single-player. You must completely exit a level to adjust resolution or sound.