Eastern Front is a very good solitaire expansion for the Conflict of Heroes series that in many ways improves upon the gameplay of the multiplayer version.
The refresh / spent rules in this version are certainly better and more intuitive and the rumored enemy aspects are compelling as are the automated vehicles. My only complaint is that the wording on the cards for the Artificial Intelligence could be clearer, but this solo game is quite fun to play and much better to physically handle than most wargames that I own if not every single one.