Best Level Ever: Or more like, Best Minigame-slash-Cutscene Ever. How awesome is it that you get to chase a running away Metal Gear on a horse while dodging missiles and trees thrown at you!? A freaking lot, that's how awesome!
Fans are divided as to whether Metal Gear Solid: Portable Ops was made non-canon due to the relative lack of reference in Peace Walker. In addition, fans were also similarly divided in regards to whether Kazuhira Miller was still working with Cipher by the end of Peace Walker or whether he quit working with Cipher after Paz Ortega Andrade attempted to launch a nuke at the East Coast under what is implied to be their orders, although the ending and the call itself suggests the latter belief is true.
Some fans of the series were divided over the boss fights. Some saw the need to procure ammo by calling it in as a mechanic that added tension, others found it just wasted time. This was especially true when fighting bosses in single player, where there would never be enough ammunition in the field for you to win the battle.
Additionally, the bosses were all armored vehicles or AI, rather than single humans with superpowers. It does provide the game with a more serious tone, but not everyone liked this detraction from the rest of the series.
The game being broken up into short missions. Some think that it makes sense for portable play, and it keeps the pace up. It also allows going back to Mother Base in between missions. Others feel that it destroys the tension, as keeping track of your inventory is no longer an issue (ammo is never truly scarce), and stopping the action every 20 minutes breaks the game's flow.
Disappointing Last Level: Some fans found Chapter 5 to be too short and straightforward. Others found it to be more analogous to an "epilogue" to the game, rather than chapter, and thus not so much disappointing as aggravating enticement for what the next story will bring.
It's Easy, so It Sucks: Some complaints towards the game consider it too easy, since ammo is replenished between missions and enemies. Stealth is not as necessary when you always have more than enough ammo to kill everyone on a map. That said, even detractors don't think the game sucks, but it's merely one of its weaknesses.
Ensemble Darkhorse: One of the early game powerful soldiers you recruit in the game is named Alligator. He quickly became the MSF member. Meaning that he is most likely Venom.
Remember that little music video where Paz sings her theme song on top of Mother Base? It's the exact same area where you fight her, with the song as the background music.
The Tactical Espionage Operations trailer has Kazuhira Miller explaining to Big Boss about their potential future role in the economy, as well as Big Boss explaining that they probably shouldn't have gotten involved in the first place because people are going to get rid of him. It becomes a heck of a lot more harsh after beating the game, as this was actually part of the second ending, a few hours after defeating Paz, where Miller ends up admitting to his involvement in Cipher's scheme.
In a briefing file about Ruinas de Xochiquetzal, Paz mentions after Big Boss mentions he'd show respect to the temple only if the mood strikes him that he has no one to blame but himself if Xochiquetzal strikes him down for that defiance. That line becomes a lot less funny when one of the lines that Paz states during her fight against Big Boss is "You have no one to blame but yourself!" when firing ZEKE's rail gun at Snake.
Miller's English voice actor is British-born Robin Atkin Downes, which is ironic when you take into account of the fact that about 31 years later, British-raised Liquid Snake does pose as Master Miller.
The Stealth Camo, the Infinity Bandana, and the Soliton Radar. If it's any condolence, usage of the Stealth Camo won't allow you to S-rank missions, the Soliton Radar isn't useful until Rank Five, and the Infinity Bandana is acquired after a very hard Custom AI fight. If that wasn't enough, they also require a very long time to develop, too.
In Outer Ops, the Kampfpistol (a Nazi flare gun modified into a grenade launcher here) does 5000 damage to everything. Vehicles and enemy soldiers included, one-shot killing them (if not dropping their health to near-dead).
While in Versus Ops, the ADM65 could count as this. Most assault rifles specialize in either low recoil or high damage, but the ADM has both of those with no clear weaknesses. No wonder everybody uses it, to the point it can become a bit jarring to other players who actually decide to give the vast number of other weapons an opportunity.
The M134 and the M47 are this for boss battles. The damage they do is just something to behold. Combine with the bandana and boss battles become easy.
The Fulton Carl Gustav is an essential tool for S-Rank runs on boss battles and can allow you to complete at least one extra op in seconds.
Holding up enemy soldiers causes them to permanently lie down on the ground even if the player character walks away for some time. This tactic is especially useful because for some reason the guards will never tell held up comrades to get up.
Kidnappers, tiny flying robots that can shoot machine guns at you or, if close enough, latch onto your leg with a grippy claw on a cable. They're never a serious threat head-on, but they're just distracting enough that they make facing tougher opponents much more dangerous, because while you're hanging in the air trying to get down, everyone else is shooting you. They get extremely annoying during the infiltration of the Missile Base - chaffing or shooting down one causes a caution mode. And they're placed in areas where you can't really hide unless you've got a box... and even then, it's a wait. They're also much more mobile than previous UAVs in the series.
Armored Peace Sentinel soldiers during custom vehicle battles. On their own, with just machine guns or assault rifles? Fine. But at higher difficulties? They start blowing you away with rapid succession rocket fire, practically playing hackey-sack with Snake's body using explosions. Even worse are the SPAS-12 wielding escorts. At least, the rocket soldiers will pause to stop and reload their weapons and will be unable to attack you if you get too close to them. Not so much with the shotgun ones, who will never stop their barrage of blasts, stunning you at every second and cancelling many of the actions you try to do.
The damn Velociprey in most of the Monster Hunter missions. Not allowing you to reload? Getting in your way of firing potshots at the bosses? Leaping on you at the most inopportune times, knocking you down just as the boss is about to do something stupid? Just being an annoying part of the bosses? At least they let you cook up your rations. The funny thing is, they're faithful to their roles in Monster Hunter - being annoying pricks.
Scouts are particularly annoying to deal with when attempting to use CQC on them. They can counter with fibre wire to strangle you. Worse yet is that they can easily detect you even when using a high-index camo suit and night vision goggles. Careful stealth is key here.
In Metal Gear Solid 2: Sons of Liberty, Revolver Ocelot was fully complacent in the Patriots' S3 Plan and was implied to be involved in the threat towards Olga Gurlukovich's child's life if Olga didn't cooperate. In Peace Walker, Ocelot himself was later revealed to have been under Sunny's position when The Boss and The Sorrow had their final battle at Dolinovodno.
Anything involving Huey in light of his actions in Metal Gear Solid V: The Phantom Pain, where he becomes less of an Otacon-clone and more of a callous monster; it makes you wonder exactly how much truth there is to Coldman's comments regarding his plagiarism and exactly how skilled Huey is, given Skull Face's team are able to complete their Metal Gear without him.
Les Yay: Paz's 5th audio diary entry. Strangelove blatantly hits on and molests Paz before the latter gets a chance to react. Paz doesn't mind. In fact, she's confused and finds it enjoyable. It reads like a yuri lemon.
Memetic Molester: Paz's diary reveals Strangelove groped her under the guise of applying suntan (Strangelove nearly fainted). Then she gets a cold, and then Miller tries to serenade her, and then exclaims that suppositories are good for colds... and then takes off his pants. And after that, Strangelove comes by with an "Indian remedy" that you rub on your chest.
Interestingly subjective: many might dispute when or indeed if Naked Snake has crossed this in the prequel continuity so far. When you consider that he's running a mercenary company that will fight for virtually anyone with the money, it seems that if Big Boss didn't cross already, he's right at the edge. Most of his dialogue in the game suggests that, at the very least, he's developed a very fatalistic outlook of the world, without even the hope for a better future that defined his son's career.
Unambiguous with Hot Coldman. His very first on-screen appearance has him going beyond the Moral Event Horizon by shoving a paraplegic down the stairs, and he only gets worse from there. And that's even before you find out that he was the one behind the events of Operation Snake Eater.
In a cruel twist, The Boss's horse must be euthanized by the player while also shooting The Boss again in a flashback, one right after the other.
How you destroy the Mammal Pod. Basically, you go inside Peace Walker and pull out all the AI memory boards, listening to a progressively deteriorating voice of The Boss. To put this in human terms, you're going inside her brain and ripping chunks out of it until she's completely lobotomized.
Paz - who we later learn is doing her utmost to fight everything she feels for Big Boss and MSF, turns on you in the finale with a mocking, heartbreaking "Say peace!" that goes against everything about her character prior to this.
Polished Port: The HD Edition of the game for the PS3 and Xbox 360 has improved controls thanks to dual analog sticks. Being ported to consoles with proper online support makes the versus and co-op multiplayer a viable option.
Paz. Most find her Moe persona extremely saccharine and more annoying or creepy than cute. Post-reveal, she becomes more of a Base-Breaking Character, as she is either Rescued from the Scrappy Heap by her tapes and true role in the story adding a lot of nuance to her character, or comes off even worse due to her betrayal of MSF and attempting to frame them by launching a nuke at the U.S. There's also the fact that she throws the player on a wild goose chase every time she frees Zadornov.
Chico is not particularly popular due to getting captured, selling his teammates out and being seen as little more than an annoying Tagalong Kid.
Huey Emmerich, a poor man's Otacon. Whereas Otacon's considerable angst made him The Woobie, in Huey's case, while he does have some legitimate grievances, many players just see him as selfish and Wangsty instead. Mind you, this is all before The Phantom Pain.
Scrappy Level: The torture chamber escape. In a throwback to Solid Snake's escape from prison in the original Metal Gear Solid, there's more than one way to escape, but the game doesn't flat out tell you what they are, instead just expecting you to look around the room for unusual prompts, which irritates some players, and once out, you're practically naked (and literally naked, too, at least from the waist up). Having to button mash very quickly for the first time since Metal Gear Solid, with no way to opt out, doesn't help matters. Luckily, unlike many other levels in the game, it doesn't count the torture cutscenes as cutscene interaction, meaning that if you know what to do, you can actually escape the level with an S-Rank. You will still die a lot due to how punishing the torture session is, though. If you wonder exactly what makes this part so hard, the speed you are expected to press the button is so fast that even you somehow get past it, your finger will be strained for at least a week from pressing the button so fast. And even worst, the presses are programmed so fast that turbo controllers can't even keep up.
Surprisingly Improved Sequel: Peace Walker is the sequel to Portable Ops in the sense that not only is it a Metal Gear Solid game made for the PSP, but it follows the same premise of building a small army by capturing and indoctrinating enemy soldiers. However, Peace Walker builds on virtually every aspect of Portable Ops and pretty much blows its predecessor out of the water.
Peace Walker's EMP, which negates all lock-on mechanisms and redirects your rockets back at you. Forget to bring a gun or Chaff Grenades? Have fun running around for two minutes dodging attacks because it's practically invincible at this point. It also tends to reactivate the EMP as soon as the last one runs out, unless you get lucky and it decides to do something else, like run around the back or try launching the nuke. The Custom version is even worse, as it's immune to Chaff Grenades. Bring an assault rifle.
The "Rathalos World Tour". Just as in Monster Hunter, it will get up and fly around the island pointlessly for an irritatingly long time before gliding in for a low sweep. This attack is hated simply for the fact that it wastes your time as it does absolutely nothing important while it's flying circles. Peace Walker makes it even worse than its Monster Hunter counterpart by making Rathalos use it far more often than in the latter.
Wangst: During the torture, Big Boss begs to be murdered not because of the pain but for killing the Boss even though he already knows the truth and abandoned America. In the Japanese version, Big Boss simply laughs as a result of the censorship and so his begs to be murdered come across as hilarious.
What Do You Mean, It's for Kids?: The Japanese version was toned down to get a lower age rating, as teenagers and children are the primary demographic for the PSP in Japan. Despite this, many elements are clearly not appropriate for the age group; there are a number of very suggestive briefing tapes, a mention on Miller mooning the other MSF soldiers while drunk at what was implied to be a wild party, various references to the drug trade, a lot of smoking (explicitly shown as well as implied), and the fact that there are two dating missions where the ending of the mission implies that the couple is having sex — with one party being less than half Snake's age and the other being male.
During the Date Kaz mission, if the player interrogates Kaz, he'll say "No skeletons in my... closet." Originally, it was closer to "I'm not hiding anything!"
The changes for the various promotional product placement items in the game were mostly changed. For instance, the magazines, which were originally referencing stuff like Dengeki PlayStation, Dengeki Gaming Blitz, Weekly Shonen Jump, and Weekly Famitsu, were altered to be about more serious matters, such as politics, and also to include nods to the Les Enfants Terribles children (Solid, Liquid, and Solidus).
The various Curry items were originally Bon Curry, Bon Curry Neo, and Bon Curry Gold 21. However, they changed it to Spicy Curry, Future Curry, and Great Curry, respectively, and they also redid the item description to give a history on what Curry is, and even stated that it was Miller's favorite food. With Pepsi Nex, they also altered the design so it acted as a reference to Narc Soda, the soft drink that Drebin often drank from Metal Gear Solid 4: Guns of the Patriots. Likewise, all of the items were also given some unique brand names (Tres Bien for the Men's Cologne [originally a product placement for Axe], and Taco Chips for the Tortilla Chips [which by the way was a product placement for Doritos]).