I, too, am getting bored of the same old hat that the developers are throwing at us. As an example, let us take the prime shooter of the day: Call of Duty. The parts in the series that played in World War 2 had us fight the Nazis. After that they switched to convoluted plots involving Russians (not even Communists anymore).
There are two real problems to every game's enemy, though.
One: The game is catering to Americans (Let's be honest, it does). Why would you even consider fielding an enemy that your own customers can't even find? As a result, it's always Nazis, (possibly ex) Communists or fellow Americans. In other words, it's either past enemies that you can't possibly NOT know, or betrayals. If it's not Nazis, it's Communists. Remember that Tom Clancy strategy game, End War? The "evil" Chinese faction turned out to be a lame "Rogue faction". If it's not either of them, it's Americans in some betraying role. As an example, I point you towards Modern Warfare 2. General Shepherd was an American who betrayed his country. Lame! You saw it before in games like Army of Two, even Splinter Cell. Yawn! But this is all, often, a result of reason two.
Two: A lot of developers pussy out of doing anything new. Homefront was originally set to have the Chinese as antagonists. However, it was feared that, since they are good trade partners of America, they would take offense and take their business elsewhere. So they changed it to a unified Korea. That's not even realistic. As a result of this scared behaviour (as if China is a big market for Western stuff. All their stuff comes here, dagnabbit), developers continue to rehash the same old enemies time and time again.
Some kudos go to Black Ops in the sense that they at least dared to put Cubans in their single player campaign. I know it was still Communists, but at least they weren't all Russian.
Suggestions:
If you HAVE to return to World War 2, why not try putting us up against the Italians?
I know they weren't really all that good but at least it would mix things up a bit.
I'm getting sick and tired of playing a game set in World War 2 and getting my ears stuffed with cries of "Lade nach!" and "DIE AMERIKANER!"
Likewise, whenever we get modern games, it is either the "terrorists" or Russians we have to knock out. Why not put us up against something else? Heck, a daring developer could even have the Greeks laughing at the rest of the European Union elicit a war. You don't pay your debts or start reforms? Maybe it's time to send in a repo team, whose actions provoke a war? It's far fetched but at least it's original.
As for pre-World War 2 shooter ideas, here's one: How about a Boer war shooter? You could shoot redcoats (Well, up to the point where the Empire stopped sending soldiers wearing actual red coats.) Shooting them is where American independence started, so it should be enough to draw in some Americans.
Likewise, why not create a World War 1 game? I loved the bits and pieces in the Darkness, even though that was warped almost beyond recognition. It would be great to be a character in a war where the first modern weapons of war were utilised. Getting bombed by aeroplanes, putting on gas masks, seeing a tank for the first time...It could be so good! I know this idea has the potential to pit us against Germans again, but at least they're not Nazis yet. Hell, if you really want to go to town, you do not even have to fight the Germans. You could fight the Ottomans or Austro-Hungarians. Have you ever shot any of them?
Long story short, tl;dr for you lazy bastards:
There's plenty of scope for originality, but it is not even seized by developers. They'd rather poop out ANOTHER game setting us up against the Russians. Or, hell, some "rogue Chinese faction". Failing those, there'll be zombies...