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.
Adaptation Displacement: Both Contra and Super Contra were originally released in the arcades, but the NES ports of these games are more popular than the arcade version.
The upgraded version of the machine gun in the arcade game Super Contra has a ridiculously fast firing rate that allows you to wipe out bosses in a matter of seconds.
Brad Fang in Hard Corps with his Psychic Blaster (fully charged). Takes down bosses in two or three blasts. And considering that there are lots of bosses in Hard Corps... Brad is like designed to break Hard Corps, his other arsenals include a short range explosive punch which hits a lot for short range, and his upgraded first weapon is a much more rapid Spray Burst which decimates enemies real quick, and his other weapon is a mid-range flame thrower that moves to wherever Brad changes his aiming...
In the same game, Browny is half the size of the other characters, lowering the chance of getting hit tremendously, has a double jump and is in possession of the Electro-Yo-Yo: a homing, long-range electric spike-ball-tipped beam that pierces through every single obstacle and defenses in the game and deals insane, continuous damage. You hardly need to aim with the thing, allowing you to concentrate on just dodging.
In Contra III: The Alien Wars, the most powerful weapons in the game include the Laser Gun, which, while it fires at a slow rate, pierces through enemies and kills bosses faster, as well as the Fire Gun, which does high damage to enemies and kills bosses in seconds if you aim at their weak spots. Then there's the Crush Missiles, which are supposed to balance their incredible damage with a slow firing rate and not quite fullscreen range, but since the game allows you to instantly switch between two weapons, rapidly spamming two alternating Crush Missiles makes every boss a joke.
By lesser extent, the heatseeker gun, even if it is weak compared to the other two, because you don't have to worry about aiming if you hold "Y"
Neo Contra has Weapon Sets D and F as well as Jaguar's katana. Set D has a Lightning Gun that can One-Hit Kill many enemies, the secondary is a hard hitting bazooka that does massive damage against bosses and stationary objects, and the lock-on weapon is the Heaven's Laser, which is absurdly strong, never misses, and reloads stupidly fast, making things that need a lock-on utter push-overs. Set F has the GV Laser (named after Gradius V) which fires a constant laser beam with a ridiculously long range. Jaguar's katana is another powerful weapon, because it can take out bosses in a few swings if you get up close to them.
Ho Yay Bill and Lance, especialy how their bond practicaly moves th story in Shattered Soldier. Also, in the European Gryzor contuity, the title is from their shared surname, as if they were a married couple(well, they could be also siblings, but that wasn't never clarrified, and the subtext remains)
Genbei "Jaguar" Yagyu and Bill in Neo Contra, especially in joke ending. To clarify, they swim in space, only in loincloths, while Bill holds that of Genbei, and to add a cherry on top of this all, there are sounds of gay sex in the background.
In the original Contra Hard Corps, there is a joke ending, where the player character is transported to prehistoric earth, and becomes a monarch of proto-humans, with one of the females being the player character's queen. This happens even if you play as Sheena. Of course, it also happens if you play as Browny.
The arcade versions were intentionally made to be short, as most arcade games are meant to play in short sessions. A perfect playthrough of either game can be done in less than ten minutes, which is an ideal time period if you're a kid in the Eighties waiting for his mother to finish her grocery shopping.
Nightmare Fuel: Most of the Contra games. There are Womb Levels, cities being blown up, and very creepy looking aliens. Probably the most disturbing boss in the series is Shadow Beast Kimkou, the final boss of Super C and one of the mini-bosses in the final stage of Contra III: The Alien Wars that has a human face for its mouth.
You think that's bad, wait until you see the final stage of Contra 4. Starting off with hundreds, possibly thousands of human corpses in the background, you inevitably end up inside Black Viper. Whose (initial) innards are composed of human flesh and still-moving people. The rest of the stage's blood and traditional Womb Level designs don't help either.
Most of the bosses in Contra: Shattered Soldier, but the ones that stand out are the bosses of Stage 1 and 4. For the first boss, at first it looks like you're going to fight the helicopter robot that attacks you throughout the stage, but as it charges its attack, the real boss, which was also the first boss in Contra III: The Alien Wars, drops from above and promptly crushes the robot. Do enough damage to it, the boss will turn around and reveal a hideous, distorted melting human face that attacks by throwing up acid on you and snorting out bugs and worms. The fourth stage boss is a fish that has a zombie-like human face, and it's ugly.
One of the first mini bosses you fight in Neo Contra is a huge plant-like monster with a distorted human head/face inside its mouth. It appears when a helicopter is about to attack you, only for that monster to come out and eat the chopper before attacking you with acid, puke, and bugs.
Porting Disaster: Contra: The Alien Wars for the Game Boy and Contra Advance for the GBA.
Scrappy Mechanic: The use of both dual screens in Contra 4. In a game series where the player character can't take much punishment, the lack of visible space between them (to see incoming enemy bullets) can hinder things a fair bit.
Uncanny Valley: One of the final bosses of Contra: Hard Corps is an alien whose first form has a face resembling a human woman that distorts hideously when hit.
There's also the Jinmen-gyo ("Human-faced fish") from Contra: Shattered Soldier. Yikes.
What Do You Mean, It's Not Political?: At the time the earliest games were released, there was controversy over the US, under Ronald Reagan, supporting rebel groups in Nicaragua called the Contras, short for Contrarevolucionarios, or "Counter-Revolutionaries." This caused some minor controversy and may have contributed to European release of the arcade game being titled Gryzor (since support for the Contras was considered right-wing and heavily opposed in Europe) and why the NES version of Super Contra and the Game Boy Contra game were retitled Super C and Operation C respectively.
Woolseyism: The localizations of the first two NES games and Operation C changed the setting from the 27th century to the then-present (as well as the names of many of the characters). This became problematic when Contra III featured an obviously futuristic setting, so they had to change the main characters' name and claim that they were the descendants of the previous heroes.