Unreal Tournament has voice control in single player (had it in 2004 I think - haven't played since then). It was for pretty basic stuff like telling the bots to defend here, attack, turn over weapons, follow, and so on. It worked fine. The recognition was quite reliable, although obviously the more commands you add the less reliable it gets, because there is more potential for confusion between similar sounding commands.

It would be a nice touch if rallying troops actually required shouting abuse at them.