This game is set in the still under-represented Eastern Front of World War II, and its core mechanic is brilliantly based around lines of supply, rather than clicking on things until they run out of hitpoints.
The core game is set in the 1942/43 Stalingrad campaign, and each map of the scenario is an intricate (but ultimately comprehensible) puzzle in which you need to figure out how to maintain your own lines of supply, while cutting off the enemy’s. As in the real war, units that are cut off from their supply lose their effectiveness, so the game is about cleverly taking advantage of this mechanic.
It also has a very attractive visual style for a hex-based, turn-based game. The game is a pleasure to look at, and all the information you need is easy to spot, and easy to read. It is a great example of how to design an abstraction of real-world systems into something fun, engaging, and playable. And it will challenge you.