Vietnam was done plenty as well with a BF Vietnam in 04, expansion for Bc2 in 2010, and Black Ops in 2010. The last good WW2 game was World at War back in 2008. With the only other mentionable good ones being BF 1942 in 2002 and COD2 in 2005.
I think it's great timing for another good WW2 game. All BF and COD games since 2011 have been set in Modern or slightly Futuristic times and it's getting stale.
I think the market is ready for another past set game and I think Treyarch understands this. They probably realize they are loosing older fans of the series and realize that the new generation of COD players will buy it no matter what it is. Smart move if they can pull it off.
They would have got my money anyways because I think they offer the best value with their DLC. If I was on the fence, returning to the roots of the franchise would have grabbed my attention back.