how does it compare to the Wargame series?
From my amateur play of both series:
Wargame focuses on great graphics and fun action more like a traditional RTS game.
Combat Mission has outdated graphics but focuses on detailed systems modeling of units, supply, communication and morale, and offers a great turn based WEGO model more like a traditional hardcore table miniatures wargame with lots of rules.
They are two good very differently focused series, I'm not even sure they should be compared against each other, sort of like comparing Company of Heroes to Steel Panthers.
I enjoy both depending on my wargaming mood, I just wish Combat Mission had Wargame's graphics, and Wargame had CM's detailed systems modeling and turn based mode.