Combat Mission took squad-level combat away from the hex-based game board, where it had lived for decades, and into a more naturalistic setting. Although it didn't approach the complexity of the most advanced board games, like Advanced Squad Leader, it made the genre accessible to people who aren't up to trying to follow rule books in thick binders (i.e., nearly everyone but the hardest of the hard core wargamer).
This game is about game play, strategy, and accuracy of World War II armaments, not about run and shoot and throwing massive numbers of polygons on the screen with an expensive graphics card. So it's more likely to appeal to readers of Military History Quarterly than players of the latest shooter. Although turn-based, it's actually a "we-go" turn system. It's designed so that you issue orders, then let the soldiers try to carry them out against the enemy. Each turn is 60 seconds long.
This game and especially its sequels, Combat Mission: Barbarossa to Berlin, and Combat Mission: Afrika Korps, still have an active development base of hard-core military history fans making new scenarios, so re-playability is nearly limitless.