Blitzkrieg is a real-time strategy/war game covering the ground war in Europe and Northern Africa during WWII. Similar to Sudden Strike, you fight as a commander for the German troops, the Soviet army, or the Allies in three large-scale military campaigns, one for each of the sides. Each campaign is divided into missions, and each mission is divided into several objectives. These objectives comprise things like taking a town, air-dropping a sniper behind enemy lines to assassinate a commander or even building a bridge with engineers to open an attack route.
Basically, Blitzkrieg is similar to Sudden Strike, though there are many little differences such as historical accuracy - shell penetration and armor values are based on actual characteristics, the weaponry your infantry follows a chronological timeline as the campaigns progress, and other. Blitzkrieg is also very well playable even for newcomers to this genre.