Some fan have debated as to what Ivan Raidenovitch Raikov's actual fate was, as well as whether recruiting him in Metal Gear Solid: Portable Ops is canon. Heck, there are even some who wonder if Raikov was actually related to Raiden due to their likeness.
Similar to other franchises, the fandom seems to have its divisions regarding the sequels and prequels. To simplify, there are the fans that are still sticking by the series and then there are those that feel the series should've just ended with Metal Gear Solid 4: Guns of the Patriots and that anything released afterwards is unnecessary.
A badass soldier with a strange affection and reliance on cardboard boxes is this. Metal Gear Solid 4 upped the ante with the drum barrel which had much of the same functionality plus it could be used to literally barrel over multiple enemies. Metal Gear Solid: Peace Walker seems to be taking the crazy awesomeness to even greater heights with a tank-shaped cardboard box (with a working gun turret), an ambulance-shaped box (complete with siren) that can heal people dragged into it, and a "Love Box" that has room for two. There is no implications there at all.
The entire franchise is covered in a thick layer of crazy awesome. From "poisonous Zanzibar Hamsters" to guns with infinite ammo Hand Waved by the magazine being shaped like an infinity symbol, to a Super Soldier who's covered in bees.
In Metal Gear Solid, Meryl manages to smuggle something past enemy guards who were searching her, because "women have more hiding spaces than men." Come Ground Zeroes, Paz has a bomb hidden in her stomach (which is removed without anesthetic whilst she's screaming in pain), and a backup hidden in her vagina, which kills her and puts Big Boss into a coma for 9 years).
Big Boss himself helped found the Patriots, only to have them spiral out of control on the side of his former best friend Major Zero. Slowly playing the government from the inside, Big Boss planned to create a world of war to honor soldiers forever. Having a loyal soldier who took the name Venom Snake used as a double to believe he truly was Big Boss, Big Boss used the man and his plans as a diversion while he focused on building his own nation, effortlessly playing his enemies for years and decades while forming Outer Heaven and later the nation of Zanzibar Land. Even surviving his own supposed death, Big Boss returns to find his plans have come to fruition to bring down the Patriots and makes amends with his son and clone Solid Snake before peacefully passing away by the grave of his mentor, The Boss.
Revolver Ocelot, also known as Shalashaska was born to the infamous Boss as Adamska and spent his youth as a double agent for the CIA and NSA while undercover. After managing to deliver the Philosophers' Legacy to the U.S., Ocelot begins to despise the puppet masters of the world, the Patriots, and seeks to bring them down. Betraying and manipulating every side he joins, Ocelot even uses drugs and psychotherapy to make everyone think he is possessed by the spirit of Liquid Snake, knowing what the Liquid persona will do to allow him to destroy the Patriots, eventually hijacking the plans of Solidus Snake and forming his own group. Even when defeated, Ocelot still achieves his goal of defeating the Patriots and ends his life in a final battle with his archenemy, Solid Snake, having been only loyal to the dream of his mother's successor Big Boss to the end.
Senator Steven Armstrong. See his game's page for details.
Each one of the Patriots crosses it at one point or another, and that's just with the human founders. Going by the AIs, the AIs probably were already on the other side in a very short time, especially given the fact that not only were they the ones who masterminded the Big Shell Incident as well as the mess that was the war economy, but the Head AI also implied to Raiden that they viewed humanity as nothing more than tools and weapons for them to discard once they no longer serve a use.
Vamp's pointlessly cruel murder of poor Emma Emmerich, Otacon's adorable little sister.
Major Zero. He had Paz Ortega Andrade attempt to get Big Boss to rejoin Cipher (a.k.a. the Patriots). Snake refused, so what did Zero do? He also ordered Paz that, should Big Boss refuse, she frame him and MSF by having her launch a nuke via a hijacked ZEKE at the East Coast, and then pinning them as an extremist cult.
Solidus Snake revealing that he was the one who murdered Raiden's parents and took him in to train him as a Child Soldier, condemning him to a life of trauma and ensuring he'll never have a normal life certainly counts as well.
Come Ground Zeroes and The Phantom Pain, Skull Face went flying over it
Narm: The series makes heavy use of Bathos to contrast its melodramatic moments with comedy, but it has plenty of unintentional drama killers too, to the point where it has its own page.
Narm Charm: That being said, a not-insignificant number of fans love Metal Gear precisely because of the melodramatic acting, insane plot twists, stilted exposition and heavy-handed messages.
Periphery Demographic: The series is extremely popular with women considering it's basically a crazy Rated M for Manly action movie in video game form. Yes, even the strong male bonding is verbatim action movie. Plenty of kids like the series too, helped by the fact that My Little Pony: Friendship Is Magic referenced it and a large part of the brony demographic grew up with the early Metal Gear games. Some part of it is also due to Snake's status as a veteran of Super Smash Bros., exposing him and Metal Gear to a much younger fanbase in the process.
Several plot elements and set pieces used Metal Gear 2: Solid Snake reappear in Metal Gear Solid, with no comment from anybody. Metal Gear Solid 2 returns the favor and cribs off of Metal Gear Solid. This time, the lead character is well aware of this and won't let the player forget as the storyline spirals inexorably towards its Mind ScrewGainax Ending. Part of this has to do with the (then) low profile of Metal Gear 2 and the megahit status of Metal Gear Solid.
This is done purposely across the entire series; There are similarities between Big Boss and Solid Snake's entries into the series that are done to emphasise their similarities and show that Big Boss took the wrong path.
According to the director's commentary, the English localization team apparently did not like EVA due to some parts of her behavior. It doesn't help that the player has to assist her in the most tedious part of Metal Gear Solid 3 and that she appears only in one act in Metal Gear Solid 4 which is considered one of the worst parts of the series.
Raiden's girlfriend, Rose, who's received hatred largely for her relationship drama with Raiden, some of which wasn't written well, as well as a mixture of Die for Our Ship and Annoying Video Game Helper feelings. Not to mention the fact that people rarely take kindly to anyone that actually waits until her lover is off at a safe distance - trying very hard not to get killed - before steam-barraging him via digital communication with everything that's bugging her about their relationship. Granted, such an idea could work out with ensuing hilarity. It's mitigated in Metal Gear Solid 4, where her romantic relationship with Raiden is downplayed and she doesn't show up too often, but that doesn't quite count as Rescued from the Scrappy Heap.
Signature Scene: The notorious moment when Psycho Mantis actually checks the gaming console memory card and knows what games the player has been playing.
While a lot of video games are content to simply let players have fun and let them learn something from the experience if they so choose, this series hammers its players over the head with complex philosophy and hard-hitting truths about the way war works that even most novels shy away from. And it doesn't stop. The repetition may seem a bit like overkill, but it's exactly what makes each game's message so effective, because it will not let you forget. Check out the trope page for more details.
Metal Gear Solid 3 is an excellent example. It constantly drives the point that enemies are not enemies in absolute terms and that enemies today may be friends tomorrow and vice versa. The game's ending makes this point all the more poignant.
Suspiciously Similar Song: The "Metal Gear Solid Main Theme" is a more heroic-sounding rendition of Georgy Sviridov's classical piece "Winter Road". The "Metal Gear Solid Main Theme" was first composed by Tappi "TAPPY" Iwase and later remixed in by Harry Gregson-Williams for Metal Gear Solid 2. Metal Gear Solid 3 was the last game to use it; after that came out, someone connected with Sviridov's estate made the infringement known, and Konami got cold feet, at least enough so as to have Gregson-Williams file the serial numbers a little further off in Metal Gear Solid 4's incarnation of the theme.
Unconventional Learning Experience: How often do you learn about nuclear weapons, ICBMs, gun mechanics, genetics, psychology, philosophy, Cold War politics, PTSD, etc., all in one video game franchise? Even better: how often do you even become interested in and curious about these concepts?
Meta example. The teaser site before E3 2009 showed this image, and many fans wondered who the hot chick in Raiden's armor was. Turns out it was Raiden. In addition, a lot of fans believed it was Sunny, due to the eyes and hair.
Vocal Minority: There is a sect of Metal Gear fans who, in the wake of the Konami and Kojima controversy, have begun to violently shout down anyone who criticizes either the series or Hideo Kojima, regardless if said criticism is legitimate or not.
How Old Snake (and quite a few players) sees the predicaments of the Beauty and the Beast Unit. It's part of the reason why he doesn't really give a crap and why he's annoyed whenever Drebin comes in to explain their origins.
Fortune. Ocelot awesomely calls her out on it, saying that she was "hamming it up as the tragic heroine".
The Woobie: Nastasha, Otacon, Emma, Meryl, Olga, and Stillman. Also, Gray Fox and Raiden as Cyborg Ninjas. ** Gray Fox and Raiden as Cyborg Ninjas.