Everybody likes to be the hero, so most games won't allow you to play the other side's point of view; after all, if you command the White Hats to victory in the Regular Mode, then you're likely to cause a time paradox if you play the Black Hats' mode and help them win, right?
This is especially obvious in WWII-themed First-Person Shooter games; it is usually the case that even though you can play both the Allied and the Axis sides in multiplayer, the single-player campaign allows you to play only as the Allied side. Whether this is because developers believe that players will not or should not be allowed to play as the bad guys is difficult to say, but it is worth noting that Real-Time Strategy games, flight sims, tactical wargames and grand strategy games usually allow you to play the Axis in single-player mode. This may have something to do with the player being more removed from the action in those types of games as well as just how awesome German machinery were. (Of course, it might just be because the Axis... well, you know... lost. And then there's the whole Nazi thing...)
Even if the bad guys get a campaign, it's not likely to be canon.
Compare No Swastikas, Videogame Historical Revisionism, and No Canon for the Wicked.
The Call of Duty games set in WWII allow you to play as a soldier on the U.S., British and Soviet sides - playing on the German or (in World at War) Japanese sides is only allowed in multiplayer. Probably because of the controversy that would ensue if players were able to be Nazis.
The first two Brothers in Arms games, also set during the Normandy campaign, feature campaign play solely from the perspective of U.S. paratroopers, while including single scenarios that can be played as the Germans.
In Rome: Total War, you can play as any faction in the skirmish mode, but only the Romans are available for the campaign at the start of the game. After playing with the Romans for a bit you can start to unlock other factions for the main campaign, but still only about half of them. This is mainly practical: the other factions either stand no chance of winning (small, insignificant nations), exist only for the sake of storytelling (the Senate has no territory and apparently infinite population) or don't make any sense (all nonaligned towns and armies are considered by the game to belong to the "slave" faction - it will honestly try to make this work for you if you unlock it with cheats, but running an absence of a government misses the point a bit, and you don't count as having any territory or population because nobody in your faction is aligned with you... wait, what?).
A common feature in Tabletop Roleplaying Games are rules that either outright forbid evil characters, or at least strongly encourage the Gamemaster to allow only good or neutral characters. The new edition of Dungeons & Dragons, for instance, lists the good and neutral deities up front in the character creation section, while setting the evil gods firmly in the 'know your enemy' part of the book.
This, of course, has no effect on some players and DMs, who create all-evil campaigns frequently and with panache.
The Dungeons & Dragons based RTS game Dragonshard, has a campaign for the humans and the lizardfolk, but not for the Umbragen.
In the popular MechWarrior video games, most of the campaigns are played in the Davion/pro Davion POV. In Mechcommander 2, Liao and Steiner is seen as cruel tyrants ruling Carver V with an iron fist and Davion wants Carver V to be independent (read: Client state), in a galaxy where morality is grey and black, Davions tends to be portrayed in a good way here. The Steiner ending in MechWarrior 4: Mercenaries is seen as bittersweet as the character abandons his company to become a Clan warrior and is the only time his operator doesn't agree with him. If not, then you are a Davion pilot.
There is also another ending in which you STAY with your Merc group and set up a base somewhere in the Chaos March, and remain neutral from then on. You DO have to be pro-Steiner for the game to get there, but it isn't bittersweet, ALL endings conclude with a mention of the Word of Blake jihad, and FYI: The MechWarrior games take their canon from the BattleTech books, so you kinda can't fault the games for making Davion win even if you're with Steiner.
It is more about how Microsoft painted the Davions in a much more white portrayal than Steiner or the other houses. It was subverted in Black Knight where you are a Steiner pilot in a what-if Ian chose to find weapons rather than saving his sister.
The Inner Sphere as whole gets this in MechWarrior 3, where the Star League-aligned commando team operates against Clan Smoke Jaguar—easily painted as an evil faction after their massacre of over a million civilians at Turtle Bay. No Clan campaign for MechWarrior 3 exists. Subverted with the sequel, Pirate's Moon, where you may elect to play as Susie Ryan's pirate team. As might be expected, the pirates are full of rebellious loudmouths and violent thugs.
Also true of two early BattleTech strategy games, the Crescent Hawk duology. In Crescent Hawk's Inception, you play as Steiner pilot Jason Youngblood, and much of the story mode takes place against the Draconis Combine. In Crescent Hawk's Revenge, you again play against the Combine and later the Clans.
MechWarrior 2 and its sequels have toyed with this trope. The original game has campaigns for both of the central warring factions, Clan Wolf and Clan Jade Falcon. The first sequel, Ghost Bear's Legacy, firmly puts the player on the side of Clan Ghost Bear, but the player's enemies are numerous and varied instead of simply the same faction as per the original game. In the final member of the trilogy, Mercenaries, the player is a mercenary who may elect to take missions for whatever factions offer them. The Federated Commonwealth, Draconis Combine, Free Rasalhague Republic, and even independent factions like corporations and Comstar offered contracts. It was not uncommon for players to spend a few months shooting up Draconis Mechs, then turning around and raiding a Fed-Com chemical plant. When the Clans show up, though, everyone bands together against them and you ultimately fight to save the Draconis Combine capital world of Luthien.
To be clear, this is not restricted to the video games. The entire Battletech extended universe paints a few factions as the good guys. Most of the books are written with the Davions or Wolves as the good guys. Of the ones that don't follow them, they usually follow a minor character or mercenary unit who will be important to the main storyline later.
X-Wing was naturally about the exploits of the heroic Rebel Alliance, and as such featured no campaign for the bad guys. The sequel TIE Fighter, reversed the situation, with a campaign for The Empire and none for the good guys. Most of the time, however, you were actually fighting Imperial traitors, not the actual Rebel Alliance.
Taken to an extreme in Americas Army: although the multiplayer element features Americans versus an enemy force, every player is portrayed as American in first-person, with the role of the enemy taken up superficially by whichever side is "not yours". This creates some interesting fractures where, for instance, the "American" player armed with his M16 appears to opposing players as an "OpFor" with an AK-47.
Which (probably unintentionally) underlines the fact that no-one is evil or unjust in their own eyes, and is also alarmingly reminiscent of the Outer Limits episode "Hearts And Minds".
In Halo: Combat Evolved: Anniversary, ODSTs were announced to be allies while playing as a SPARTAN in Firefight. "Does that mean we can kill them as Elites?" is a signature fan statement to any article or video announcing this. No, but why should that stop you?
In the Homeworld franchise you only get to play the Exiles/Hiigarans in single player, but you get to play either side in multiplayer. The first game had an interesting take on this, as you could play as the canonically evil race - but doing so simply made both sides swap roles, so you experienced the exact same story with defence frigates instead of drones.
Subverted somewhat in Killzone: Mercenary where you do fight alongside the Helghast in the campaign, albeit as a Private Military Contractor rather than an actual Helghast soldier.
Played With in the last level of Shadow Fall. While you aren't playing a full blown bad guy, Echo/Maya Visari is a part of the Helghan regime and she ends up taking down corrupt ISA official Thomas Sinclair.
In Bungee's RTS series Myth, the player can only play as the Human faction in the single-player campaign mode.
Very noticeable in the Command & Conquer: Red Alert 2 expansion Yuri's Revenge, despite the title there is no Yuri campaign. You can choose whether he's defeated by the Allies or the Soviets (and once again which ends up dominant over the other) depending on who manages to hold the time machine at the start of the story. You'd think after doing all that work to build a third faction they'd give it a campaign but nope.
Rooting around in the game files shows audio files containing briefings for Yuri missions, including one where you play Yuri during one of the missions undertaken in the Allied campaign. There's not enough to warrant a full campaign though, suggesting they ran out of time. That, and the faction is so unbalanced that the campaign'd have been a cakewalk anyway.
Ground Control and Ground Control 2 both let you control two different factions, in two different campaigns, where one campaign follows on from the other. However, in both games, you are still always the good guys - in the first game, both sides are revealed to be evil (with the exception of the two protagonists and their forces). In the second, the NSA and the Virons are good guys, and hence controllable, while the Imperials are never controllable at any point in the game. Worse, this actually extends to skirmish and multiplayer.
Pokémon is especially cruel as you are actually invited in every game to join the antagonist team, and yet you are forced to decline.
In Brütal Legend you only play as the Ironheade in campaign mode. The Tainted Coil don't even have a proper battle against you to demonstrate their army's mechanics, but simply spawn basic units directly onto the battlefield. All three factions are playable in multiplayer, however.
A number of fans were hoping that Dissidia: Final Fantasy would include a story mode for the villains, but it was not to be. You can however play as the villains for the side storylines, Distant Glory and Inward Chaos, but the character you play as has no impact on the plot. The announcement that the sequel would change this caused much rejoicing... except that it didn't and 012 still had no villain campaign.
Literally played straight in Left Behind: Eternal Forces. The player can only play the Antichrist's Global Community Peacekeepers in multiplayer. But given its intended audience (and its quality), who would want to do that?
In Battlezone, the American forces get a full-fledged campaign. The Soviet forces just get a bunch of unconnected missions.
Aztec Wars has only a campaign for the Russians. None for the villainous Aztecs or the uneasy allies, the Chinese.
An example from Tabletop Games. In Shadowrun, in early editions, it was explicitly made clear that PC shadowrunners were not allowed to be genuinely evil, and the rules enforced this by making Karma synonymous with Experience Points. You couldn't get XP through doing evil deeds, period, and you could sometimes buy XP by donating money to soup kitchens. This was removed in 4e and returned in a less-emphatic form in 5e (where evil deeds earn less karma than good ones). In addition, learning Blood Magic instantly turns you into an NPC, no exceptions, because good shadowrunners don't do that sort of thing.
Averted in Deus Ex: Invisible War as you can chose to assist any of the power players presented without exception.
Averted in tank simulations as a whole since there is something alluring about German armour blitzing though enemy lines.
Averted in Star Wars: Empire At War. You get to play as the Empire, though the ending is non-canon. The expansion, Forces of Corruption, has the Zann Consortium as the only faction available in Story mode.
Averted in Warcraft and its sequel. Semi-averted in later RTS games by Blizzard Entertainment. You get to play as Terran and Zerg and Protoss in StarCraft... but it's a single storyline, as opposed to the earlier games where playing on one side was the entire story, the other side's game being an "alternate universe" of sorts.
The whole thing gets taken to the next level in Warcraft III, where no matter which race's campaign you get to play in you get to kill at least once race that you were so happily guiding to victory before, with the Night Elves campaign allowing the player to dabble in killing some of all three other major races present in WC III, and then some.
Averted in Battlestations: Pacific. Not only is there a full Japanese campaign, but it takes a complete Alternate History approach where they go on to win the war. Including an ending where the Americans sign the instrument of surrender on board the battleship Yamato in San Francisco Bay.
Averted throughout most of the Heroes of Might and Magic series. In the 1st game, there are four available lords to choose from, two of which the game identifies as 'evil' and two which are identified as 'good', though given that the campaigns are identical except for lacking the scenario that is about conquering the lord you play as there isn't much to indicate their actual morals (except for the canonical victor, the Knight Lord Ironfist, which the manual paints in an ambigious light). In the 2nd game you can play as Archibald Ironfist's top general though it's a non-canon path. The 3rd game and its expansions have quite a few campaigns that let you play around with the evil armies (and those are canon). Mostly played straight in the 4th game; the most "evil" main characters are a half-dead Anti-Hero necromancer who saves the world from a death god, and a pirate who spends most of her campaign fighting even worse pirates and sea monsters. The 5th game and its expansions has only one campaign with an evil main character. It makes up for it by making said character the most evil person in the franchise.
Sometimes you technically get to play against yourself as the bad guy in a good guy campaign or vice versa.
The World War II combat flight sim series IL-2 Sturmovik and its sequels/expansions allow you to fly not only for Germany and Japan, but also for the minor Axis air forces of Finland, Hungary, Romania and Slovakia. Nearly all countries that participated in aerial combat during the war are present in the games, in one way or another. It's also unusual to have a game that lets you play as the Soviet Union (sort of the Allies' Token Evil Teammate) rather than just the US or Britain.
Microsoft's Combat Flight Simulator trilogy allowed players to fly for the United States, Japan, Britain, and Germany (of course, the actual nations involved in each game differed depending on the game: the first and third games took place in Europe, while the second took place in the Pacific theater). The third game's campaign even allowed players to make changes to history (the campaign starts in March 1943, and it's possible to start an invasion of continental Europe within a few weeks of starting, or even have Germany invade Britain within a few months, depending on how good the player is).
Averted in the (Czech-made) Vietcong 2, which does have a campaign where you play as the Vietcong, although it's much shorter than the American campaign, and portrays the Vietcong in a reasonably negative (albeit ironic) light. Played straight in the first one though.
Spectacularly averted in Hearts of Iron 2, due to it featuring just about every country in existence during WWII and allowing you to control all of them; incidentally, Germany happens to be the most popular nation to play.
However, you need to score Major Victories in pretty much every mission to get the Germany Conquers The World outcome. A Minor Victory in just one later mission will end the war in a defeat or at best a stalemate.
In Panzer General II, there are campaigns for the German, Soviet and UK/US sides. The last of these has identical scenarios regardless of which country you choose, only the units available to you are different. The German campaign is the most elaborate one, with a historical success enabling an invasion to capture Savannah and culminating in an attack on the Oak Ridge facility to prevent the US from completing the atomic bomb.
Panzer General II also reenacts atrocities under your command. For instance, the first mission is helping out Franco's troops in the Spanish Civil War. If you cursor over it, one of the towns you pass through on the way to the objective is Guernica. Yeah...
Averted in Empire Earth, where both campaigns set in modern times involve the bad guys - the German Campaign leads to Those Wacky Nazis and the Russian Campaign follows an oppressive future Russia which attempts to conquer the world although you pull a Heel-Face Turn later. The former campaign abruptly ends in 1941, most likely to avoid the Unfortunate Implications of playing as a German commander during the years of the Holocaust.
Or maybe because the final mission of said campaign is carrying out Operation Sealion and bombing Buckingham Palace. There probably wasn't much else to do after that...
Averted in the ConquestsExpansion Pack of Civilization III; you can play as the Japanese in the Pacific theater and there is no European theater scenario at all.
Same with Evil Genius, of course. The genre seems very conducive for playing the bad guys. Just like Theme Hospital. Errr, wait...
Averted in a sense in Marathon Infinity. The game has multiple alternate continuities you play through, and in one of them you're an agent of the Phfor. You slaughter your former heroic human allies by the dozens.
Averted in Command & Conquer 3, as all three factions has a campaign. Also, each campaign is canon and occurs in the same timespan, so in a way the player is fighting against himself/herself.
Plants vs. Zombies: The "I, Zombie" minigame lets the player pit zombies against (cardboard cutout) plants.
The new Medal of Honor has been criticized because it will let you play as the Taliban. This is no longer entirely true. The Taliban faction still exists in multiplayer, but it's been renamed "Opposing Force".
The Steel Panthers games generally let you play with a diverse set of factions (including, yes, the Germans and the Soviets), though only the fairly major ones have their own premade campaigns. You can pit any two factions together in the randomly generated campaigns, though (which are essentially a set of random battles strung together).
Entries two, three and five of the Silent Hunter Series avert this. For similar reasons as the aforementioned tank sims, as Germany placed more emphasis on submarines/u-boats than the other World War II powers.
In SWAT 2, you can play as the terrorists.
SD Gundam G Generation DS has a Villain Route where your forces consist of the antagonists from the myriad Gundam series like the Titans, OZ, and OMNI Enforcer.
Star Wars Battlefront's Galactic Conquest mode allows you to play as any faction, though the endings, particularly in II, are No Canon for the Wicked to the point where even the Republic's ending isn't the same as what happened in the movies.
Darkspawn Chronicles is interesting in that playing the battle of Denerim as a darkspawn is vastly harder than playing it as the heroes, and the last battle where you protect the Final Boss from the main game's party, led by Alistair is the hardest battle in the game by far.
It also has Leliana's Song, in which you play through the events that led to Leliana's Heel-Face Turn.
Transformers: War for Cybertron actually encourages you to play both Decepticons and Autobots - the first half of the campaign allows you to play as Decepticons getting the upper hand, and in the second, you play Autobots trying to foil their plans.
Transformers: Fall of Cybertron does this as well, albeit with a single campaign that splits its time fairly evenly between the Autobots' attempt to escape Cybertron and the various counter-Autobot missions and factional battles of the Decepticons. Not experiencing the fighting both sides detracts significantly from the storyline's coherence.
Not averted in the demon path of Soul Nomad & the World Eaters; you don't play the part of the World Eaters, or even the later enemies you encounter, but instead play the hero(ine) as an Omnicidal Maniac hell bent on destroying EVERYTHING. (Though you do get to recruit some characters that are exclusively villains in the normal path.)
Averted in Red Orcestra 2: Heroes of Stalingrad where, apparently for the first time, you can play as the German through the battle of Stalingrad and change history by winning the battle of Stalingrad, though it will most likely be a series of maps and some flavour text instead of a full campaign, it's mostly a multi-player shooter after all.
In a particularly amazing aversion, The Lord of the Rings: The Battle for Middle-Earth actually features two campaigns. One in which you play as the forces of good and the One Ring is destroyed. In the other, you play as the forces of evil and take control of the lands of Rohan and Gondor, ending with the death of Frodo in Cirith Ungol and the destruction of Minas Tirith itself.
The base Company of Heroes game is a straight example; it contains an American campaign, but not one for the German Wehrmacht. The aversion is in the expansions. Both of the new factions in Opposing Fronts (British for the Allies and Panzer Elite for the Axis) get campaigns, but the Wehrmacht is still left out. The Panzer Elite campaign sticks to history by being set during Operation Market Garden, a historical short-term win for the Axis. In the tank-centered hero campaign in Tales of Valor, the central cast is of course a German Panzer crew (in fact, the same commander from the PE campaign, earlier in his career.)
Averted in the Sega Saturn game Iron Storm. There were 3 campaigns one could choose from, the US, Nazi Germany, and Imperial Japan. Surprisingly each one has a Bitter Sweet Ending vibe to it:
In the US ending, it plays out like in Real Life. The Cold War starts shortly after defeating the Germans and the Japanese.
In the Nazi Germany ending, Germany conquers the Soviet Union, defeats the US (and takes over the eastern half of it) and then defeats Japan in India once they become a threat. The Third Reich then pretty much rules over the entire world, although it falls apart shortly after someone assassinates Hitler.
In the Imperial Japan ending, they take over Asia, the western half of the US, and defeat Germany in India to become the dominant power. But then Japan becomes an economic slave to the US due to the American's inexpensive but high quality electronics and automobiles (basically a reversal of what happens in Real Life).
Star Wars: The Old Republic offers just as much content to The Empire's players as to The Republic's. Notably, however, you are not required to play a Dark Side character for the former and a Light Side one for the latter (though it's certainly easier).
Sonic Adventure 2 has two parallel campaigns, one for the good guys ("Hero") and one for the bad guys ("Dark"). Once both of these campaigns are beaten, a third "Last" story is unlocked in which both sides team up.
Gundam Crossfire has a Zeon campaign. Notably, it still follows the canon storyline, where Zeon is defeated and eventually driven off Earth, the main difference being that the final mission is a Pyrrhic Victory rather than an all-out defeat.
One of the selling points of Angry BirdsStar Wars II is that you can play as the villains through their side of the story.
Star Wars Galactic Battlegrounds has campaigns for both evil forces (Empire and Trade Federation) and three of the good forces (Gungans, Rebels, and Wookiees - twice, if you count the tutorial). The only force to not have a campaign is in fact composed of good guys - the Royal Naboo - because the Naboo are mostly nonviolent and only really fight in defence of Naboo itself, although this doesn't stop them appearing on any planet you'd care to name in standard games.
In Silent Storm you have both Alles and Axis to play for but the story has little to do with the mainstream of WWII and instead focuses on investigating and eventually fighting a clandestine terrorist organisation bent on world domination.
The Dynasty Warriors and Samurai Warriors series allows you to play either side of any (or just about any) battle in Free Mode, but this may be due to the fact that you actually do play with one particular side as the "protagonists" during the Story Mode.
However, the Crossover series Warriors Orochi doesn't have a campaign for Orochi's side until the sequel.
The Dark Crusade and Soulstorm expansions averted this, allowing one to play the "Risk"-Style Map as any of the factions involved in the war.
Dawn of War II goes full circle, as the campaign is Space Marines only.
Can be averted or played straight in the first expansion, Chaos Rising, where equipping certain Wargear or taking certain actions corrupts the Space Marines into following Chaos, or one can play a pure-good campaign run.
Retribution, the second expansion, continues the full circle, as each of the factions have their own campaign. However, it is the same set of missions with the same objectives. The main difference is that you get a different storyline dialogue to justify your actions.
The stand-alone expansion Opposing Fronts, however, features a single-player campaign for both British/Canadian forces and German armoured forces. The latter is set during Operation Market Garden, which ended with the Allies' defeat.
Inverted with the expansion pack Tales of Valor which single-player campaign is just about a single German tank crew during the Normandy Invasion. That's right, you're going to cut through waves and waves of Allied forces.
Another exception to the rule is the realtime tactical game Soldiers: Heroes of World War II. It features a German campaign in which you control the tank ace Wittmann and his forces during the defense of Normandy, tearing Allied tanks to pieces while hiding from their superior air power. It is notable for depicting the German soldiers you control as basically honourable and "professional" soldiers, rather than as the mindless babykillers more commonly seen. This is even more remarkable when you consider that it was developed by a Russian studio.
The sequel Men of War does the same, though it is probably not a coincidence that the German campaign takes place in the Mediterranean rather than the Eastern front.
Civil War Generals 2, the sequel, averts this, allowing you to fight campaigns as either side.
The offbeat old Civil War game North 'n South let you play as either side. The game lampshades a Confederate victory by saying, "You obviously didn't take history in school."
World in Conflict has a campaign only for the US side, with some missions where the player character commands a coalition of European NATO forces. The Soviets aren't even given any names of note (like commanders that you might face during the campaign), and there is exactly one instance where you actually hear a Soviet character speak: the game intro, where an an officer delivers a very cheesy line about feeding the vultures.
However, a downloadable expansion featuring a Soviet campaign has been announced for release in autumn 2008.
Now that the Campaign is here, the Campaign essentially goes in the same plotline as the events of World in Conflict with you in Soviet's POV where the Soviet gains ground in other parts. Orlovsky is a human face for the Soviet Forces rather than a mustache twirling villain and that the Soviets had tried to ask for aid before being forced to invade.
Inverted in the Kane's WrathExpansion Pack for Command & Conquer 3. While most games in the series have a campaign each for the Good (GDI, Allies) and Bad (Nod, Soviets) armies, Kane's Wrath only has a Nod campaign. Of course, this only makes up half the package, with the brand new "Risk"-Style Map mode being open to all factions.
While both Red Alert 2 and its expansion, Yuri's Revenge, allow you to play as the usually-evil Soviets, the expansion doesn't have a campaign for Yuri's own faction, which was created for it and serves as the main villain in both the Allied and Soviet campaigns. This is probably because the developers ran out of time, as there are files related to a Yuri-faction campaign buried in the files — but not enough to make a campaign out of.
And when we say "usually-evil Soviets," it's because in Yuri's Revenge, the Soviets are actually portrayed kind of sympathetically, having gotten their asses kicked by the Allies in the main game and having been betrayed by Yuri.
Averted in Command & Conquer: Generals, where you get to play as the irredeemably evil Global Liberation Army, a terrorist group whose atrocities (which the player orchestrates) include massacring a village to steal UN relief supplies, and launching a bioweapon attack on a civilian city.
Played with again in the Firestorm Expansion. While both factions are given a campaign, this was the first game to make it so that both were canon. On top of that, they made a pseudo-third faction, containing CABAL and his Cyborg army. While most of the units are playable in Skirmish (they're all Nod units) they're not during the campaign.
Star Wars Battlefront II only has one story mode, for the clone troopers. They stop being the good guys halfway through.
Somewhat subverted in Battle Realms. Because of the branching story style of the vanilla edition's campaign, it is possible to play as the sneaky, insidious Serpent rather than the honorable and Lawful Good Dragon clan. However the expansion campaign only allowed you to play as the Chaotic Good Wolf clan.
You can can play as hero and villain alike in Dissidia: Final Fantasy outside of the 'Destiny Odyssey' and 'Shade Impulse' story modes, but only the protagonists have playable roles in those modes.
Double averted in Jeff Wayne's War Of The Worlds. Not only are you allowed to play as the alien invaders, said invaders aren't really evil. The martians only went to war with Earth because Mars was dying and all efforts to maintain their biosphere had failed.
Triple-y averted in Lego Batman which has Another Side, Another Story just as long as the three Batman campaigns in which the player gets to take on the roles of all the villains in the game.
Since it's all about the Allied bomber, B-17 Flying Fortress: The Mighty 8th only has a campaign for the Americans. However, you can, at any time during the mission, switch from flying the bomber into any other single-prop aircraft currently airborne in the game-world, including the German interceptors launching to take your bombers down. It then becomes a case of playing the enemy within the Allied campaign.
Averted in Panzer Elite Action: Fields of Glory and Panzer Elite Action: Dunes of War. These are action shoot'em'up games (fairly similar to the tank driving stages in the Call of Duty series), and part of the single player mode are German missions. It's interesting that the briefings and the constant dialogue between the tank crew members paints the German soldiers as normal guys that do their duty, just like those heard in the Allied missions.
Weakly averted in Fallout: New Vegas. The player character can side with any of three major factions (or none), including the obviously evil Caesar's Legion (who favor subjugation, slavery, misogyny, and crucifixion, among other things). However, none of the recruitable NPCs support the Legion, two will leave the player's service if he/she follows the Legion, and one will actively shoot at Legionaries at every opportunity. Needless to say, diplomacy is impossible at this point. Furthermore, in the Honest Hearts DLC, the player has the choice to choose a violent or peaceful ends to two tribes being forced to deal with the White Legs tribe, who seek to join the Legion, yet no option to assist (or even speak with) the White Legs exists. This is especially jarring for characters who wholeheartedly support the Legion.
There isan option to assist the White Legs, but it is easily missed: go on a killing spree. If you kill a quest character, you get a quest to find the map you need, allowing you to finish the DLC without helping the non-White Legs tribes out. You won't get as many ending slides, especially if you don't kill both Joshua Graham and Daniel, and you won't get any achievements, but the alternative is there for the Legion-aligned character.
Age of Empires has a campaign for Rome's enemies in the Rise of Rome expansion.
In Age of Empires II, There are campaigns for both Genghis Khan (who even manages to invade Europe!) and Attila the Hun, not to mention covering both the Crusades-era Saracens (Saladin) and the Crusaders (Barbarossa). On the other hand, the Britons have only a few scattered missions (while being the adversaries in many campaigns), and you play as the Aztecs rather than the Conquistador Spanish.
A minor subversion in Terminator 3: Rise of the Machines. You get to play one level as the Terminator before he got reprogrammed.
In Shin Megami Tensei I, you eventually have to choose between Law, Chaos or Neutrality, picking your own view of "what is right" and imposing it upon the world; all three sides are somewhere between black and gray. However, prior to finally picking your ending, there are many examples of jerkasses who you cannot deal with diplomatically or ally with, regardless of your side. Also, notably, you cannot choose Yuriko as your romantic partner, partly because her plotline has her acting as a Yandere toward you and that wouldn't work if you could accept, and partly because she's Lilith, you're Adam, and your actual destined partner is Eve.
In Shin Megami Tensei II, at the end of all three routes, you fight YHVH. Yes, even if you sided with Law, you have to turn on Him.