This is one of a very popular series of games from GMT covering the first months of the invasion of the USSR; units are battalions through divisions, hexes are about 5 miles, and turns are two days. The system encompasses (as of 6/2001) Barbarossa: Army Group North (2000), Barbarossa: Army Group Center (1998), and Barbarossa: Army Group South (1996). Typhoon! (1995) is the progenitor of these games, and its system is quite similar, but it is unfortunately subtly incompatible with the later games.
While not simple, these games are also not overly complex and present an excellent simulation of the early war. Most of the details of the campaigns are covered in a playable manner. Perhaps the most obviously interesting detail is the sequence of play, which is asymmetrical to account for the difficulties the Soviets labored under. Make no mistake, the Soviets are going to take a lot of abuse, but this is no walkover for the Germans and both sides are interesting to play.