I have Company of Heroes and it is THE BEST WW2 rts and possibly the best WW2 game imo.
It isnt like you regular rts where you have to spend time getting resources or where there is one unit that OMGZ PWNS! or where you can build the ultimate defense. It forces the player to adapt and to use a variety of units at the same time. It is also very balanced (but of course it has a few bugs), there is always a counter to any strategy, tactic, or unit.