Well modern shooters nowadays seem to have plot twists resulting in you killing your own countrymen so.. (MW2,Conviction, uh... any others)? Any game involving 1800s frontiersmen would portray the americans as rather dickish, too, considering how both public and private american forces displaced the natives.
Brits were pretty "evil" throughout the imperial ages or whatever you wish to call them. There's a reason Gandhi did what he did, for example. They'd be rather easy to portray as evil so long as you don't mind a little archaic gunplay.