I'm not sure how the single player mode is going to play out, but I hope there is a compelling storyline. If you want to see how not to build a compelling storyline then play Axis & Allies RTS. In A&A RTS you are simply guided from battle to battle, which no indication of 'why' you are fighting it, why it's important to the war, or how it will benefit your side. A&A RTS boiled down to a list of semi-famous battles where they relied on a players knowledge of the war to understand their importance. Unfortunately 90% of players don't know WWII history that well, and have no idea of the impact nor importantance of the battles. It was never explained, and thus the players were never drawn into the storyline... because there basically was no storyline.
Does anyone have any idea on what the storyline is going to be like in Company of Heroes? How many battles there will be? Will it be a straight linear campaign mode or will there be diversion points based on winning or losing battles so it's somewhat replayable? One thing that 'should' make a WAR game unique is that a player should not be expected to win every battle. Setbacks happen, and a nonlinear campaign in a Single player experience of a RTS would make the game more dynamic and greatly add to the replayability of the game.
I mean, what if the America lost on D-Day? Maybe Germany cedes Africa, and pulls back in Russia, and is content with owning central Europe and the war is over. There's a lot of what if scenarios that would be interesting and fun to play out.