These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Breather Level: The "Checkmate" mission of Strike Force. It is in the last tier of the game, but it is easier and shorter than most of the others. It is a small map featuring two courtyards (one with the truck that has to be stolen to flee and a few enemies, the other with a lot of enemies - which can't be stealthy eliminated - and the NPC that must be killed) and a medium building above them. Stealth elimination of the enemies in the first courtyard and in the building is piece of cake (the first enemy that can be killed gives you an officer uniform); after the courtyard of the truck is cleaned, the assassination target leaves the crowed courtyard by himself to reach a car, falling into an ambush which is easy to set and doesn't alert the enemy if properly executed. Raising the alarm doesn't trigger a defeat and cleaning all enemy presence from the level isn't required.
Critical Research Failure: A French edition of Strike Force comes with a back cover stating that the game is set in 1942, "48 hours before D-Day". D-Day is the name given to the 1944's landing in Normandy. Which makes this error worse is that said event is very well known by French people.
Game Breaker: The Thief is one in Destination Paris. In Men of Courage, his capacities are very useful (he is the faster runner, he can climb poles and walls, he can unlock doors/crates, he can punch enemies, he can crawl in tiny spaces, he can ask his pet rat as distraction, he can enter building through windows) but he lacks the ability to tie knocked enemies. In Destination Paris, he as all those abilities and the mod gives him a few others: he can tie enemies, throw chemical grenades, and put bear traps. It makes him become a sort of tiny One-Man Army.
To a lesser extent, finding multiple knives for the Diver in Men Of Courage. Allows him to make multiple silent kills (so long as there are no enemies standing next to targets) from a distance and recover the knives afterwards. It can be done more quickly than the sniper's rifle and without the ammo loss too at the expense of range.
Good Bad Bugs: In Behind Enemy Lines and Beyond the Call of Duty, there are two way to cross water: swimming with a scuba gear (only available to the Marine) or using an inflatable boat (carried and driven by the Marine). Swimming underwater allows to be unnoticed, in opposite to using a boat. A bug allows the Marine to pick up his inflatable boat even if other commandos boarded it... yes, you read it correctly, the Marine of Behind Enemy Lines can carry half of the team into his backpack and even cross rivers with this burden.
Growing the Beard: Many fans of the series consider Men Of Courage to be the best game in the series, due to its balance of features and difficulty (though many enjoy the Destination Paris mod for the extra difficulty).
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The removal of hotkeys from Destination Berlin was quite controversial among fans. However, someone made a mod to remedy this.
The genre switch of Strike Force, which is a FPS Spin-Off in a RTS series.
Uncanny Valley: Men Of Courage and Destination Berlin have 3D animated portraits of the members of the team. Most of the Men Of Courage ones are fine (except the Natasha's one, which is rather ugly), but those of Destination Berlin are especially bad-looking, it gives them a kind of sociopathic badass look.
Unwinnable by Insanity: The first "Normandy" mission of Destination Berlin. It requires to destroy a lot of German stuff, but the Sapper doesn't begin with enough explosive for the mission. There is more bombs in an ammunition warehouse, which is one of the objectives to be destroyed. Blowing it will makes it inside unreachable, so blowing it first without emptying it makes the mission unwinnable.