Mengsk does mention he feels like Kerrigan is his biggest mistake, but the game leaves it ambiguous if he actually feels guilt for creating one of the biggest mass-murderers in the Koprulu Sector by doing so, or if he's just pissed off about the fact that he created the biggest obstacle to his plans. Either way, there're no more doubts about him being a bastard. For that matter, is Mengsk a hypocrite who's just trying to save his own skin, or does he genuinely believe he's the last chance of survival humanity has?
On a related note. Mengsk is considerably more tyrannical in this game than he was in Wings of Liberty, and that alone is saying something. Now, is it because of the exposure from Media Blitz and he's realized he has no reason to hide his true colors, or, in a more sinister note, has Duran been controlling him since Brood War, first subtly to make the Hybrid and now outright mind-control to try anything he can to kill the one threat to Amon's goals? After all, Whispers of Oblivion does establish the hybrid can outright mind-control an entire army of terrans. One dictator would be child's play...
The game doesn't specifically says why Kerrigan abandons Niadra, so this part of her attitude is completely up to interpretation. Did she do that because she was disgusted about what she just used her for? Or was this just a You Have Outlived Your Usefulness caused by what remained of the Dark Voice's influence? Could it be because the ship teleported to Shakuras and thus might be out of range for communication? Could it be that Amon is blocking Niadra's connection to the Swarm?
Anticlimax Boss: Zurvan is considerably easier than the preceding boss Slivan, as all his attacks are highly visible and not very fast. Slivan on the other hand constantly mass-manufactures living explosives without warning.
Many fans complained that Raynor's vow to kill Kerrigan or Fenix's death weren't mentioned in Wings of Liberty. Both are referenced when Raynor finds out that Kerrigan has turned back into the Queen of Blades. The scene implies that Raynor mentally divorces the Queen of Blades persona and Sarah Kerrigan, and that he was saying he would kill the Queen of Blades when he had the chance in Brood War. StarCraft II was about doing that without killing Kerrigan; when he sees that she's voluntarily turned back into the Queen of Blades, the rationalization seemingly blows up in his face. Hence his initial reaction.
As noted on the YMMV page for Wings of Liberty, it was pretty dickish for Raynor to kill the Tal'darim, defile their temples and steal their artifacts to sell for money. What's that? It turns out the Tal'darim work for Narud and worship Amon? Oh, okay then, fry them.
As well, some fans complained about the Retcon that the Tal'darim were just a splinter group on Aiur serving Ulrezaj and had no influence beyond Aiur's since they were stranded there, and Blizzard's explanation that the Tal'darim were a larger group that the Aiur branch was just a small part of seemed like a Hand Wave. With the reveal that they worship Amon, who is very likely the mysterious entity Ulrezaj serves, suddenly their role in the game makes much more sense.
The Umojans appearing in the starter missions could also be considered this as many fans have complained to Blizzard over the years for not giving this Terran faction any role whatsoever in any of their titles until now. And even despite their Heart of the Swarm appearance, they're still considered no more important than a nameless Terran faction. Perhaps justified. Umoja only has three worlds while the Dominion have dozens. Even the Kel-Morine Combine is gigantic compared to them. They get some light in the novels, being the faction that supported Acturus' father and the place where Valarian grew up. It is also stated that they put a lot of money and effort into making technology more advanced than the Confederacy. Still, they don't have nearly enough power to throw their weight around.
Broken Base: Much like Wings of Liberty, there are points in the game considered controversial:
Kerrigan's characterization can also break bases. One camp believes it to be a good Character Development that humanizes the former Queen of Blades who was previously known as an extremely brutal, remorseless and sadistic being. Another camp believes that her sins as the Queen of Blades are completely unforgivable and this characterization attempts to make her a Karma Houdini by trying to make her sympathetic. Another camp believes that she should just stick with the complete Queen Bitch of The Universe personality as it was a phenomenally awesome villain instead of being a conflicted character.
Complete Monster: If there was any doubt about Mengsk being one before, he definitely classifies as one now. Kerrigan is now de-infested, she and Raynor are cooperating peacefully with Valerian as they experiment on her, and he has control of Char. Perhaps he could bury the hatchet, leave his enemies alone and all could be well. Well no, he attacks the facility to try and kill Raynor and Kerrigan, is implied to be willing to kill Valerian to do it, and during the course of the campaign resorts to nuking his own bases of power, killing off his own citizens, to protect himself from the Zerg.
Mengsk: I made you into a monster, Kerrigan! Kerrigan: You made us all into monsters.
Another moment is when he callously abandons his own soldiers to die to try and kill Kerrigan and Raynor. More specifically he talks about how "all those brave men will have to die". The soldiers are confused by this....than the blasts start erupting. As the soldiers scream, Mengsk venomously tells her that Kerrigan and Raynor can "burn together."
Designated Hero: Kerrigan has been accused of this by some fans; while there is no denying Mengsk is an evil bastard who needs to be overthrown and she is more than justified in her hatred of him, a a lot of her actions during the campaign, such as killing the Protoss on Kaldir, routinely ordering her brood mothers to invade Dominion planets or attacking Protoss soldiers she seemingly has no beef with at all for the sake of Abathur's experiments, feel excessive and still villainous. Granted, she is supposed to be an Anti-Hero, and she does get mostly better as the campaign goes on, but there is a lot of debate on how justified the multitude of death she caused trying to reach Mengsk was, and some consider he is right to call her out for it.
Given what the story actually entails and reveals about her Queen of Blades persona, this trope is actually somewhat subverted. Queen!Kerrigan was essentially an emotionless, brainwashed slave of Amon's reprogramming of the zerg to make them even more hostile and vicious, and wasn't entirely responsible for her own actions. The entire game is about her trying to to preserve her new!old conscience against the desires of the zerg -who are fully revealed to be a simple Draco in Leather Pants situation, being The Social Darwinist as a species even out of Amon's control- and she finds it, becoming a full, sympathetic Noble Demon who is just as much a Restraining Bolt on the Horde of Alien Locusts as a ruler...though she's still a Villain Protagonist, just A Lighter Shade of Grey than before.
The million dollar question remains tough: Was this the way it was originally planned or did Blizzard decide along the way thy didn't want Raynor to kill Kerrigan after all because they just liked her too much? There are subtle hints in Brood War that point to both. Kerrigan being exhausted and down after her Moral Event Horizon is a clear hint to a lack of free will.
Ensemble Darkhorse: Abathur, the local Mad Scientist is rather popular, with some people filing petitions for him to be the new Zerg Advisor, which then happened with the announcement a voice pack for such will be released after Legacy of the Void. He even becomes a unique hero in Heroes of the Storm for that, being the first 'Engineer' character to have the privilege!
Kerrigan herself makes the campaign a breeze. She starts with two spells, one of which is essentially Yamato Cannon with no charge time and lower energy cost, the other an AoE stun with damage-over-time, and she has an innately high energy and health regeneration rates. From there she moves on to doubling the attack rate of allies and giving them +200 max HP for a time, spawning overlords instantly and causing them to give double supply, making drones hatch two from an egg, spawning six banelings at a target location, summoning an army of primal zerg instantly with drop pods, and healing allies nearby. If you know how to use her abilities properly and micro her carefully, Kerrigan can solo a lot of missions. As an added bonus, while Kerrigan is far from indestructible (in fact on the last few missions she die very easily if the player is careless), she respawns for free at your main hatchery/lair/hive sixty seconds later. And she will do this forever.
One of her abilities creates Broodlings whenever she kills a unit, either with her attack or with an ability. One of her ultimate abilities, Apocalypse, lets her deal 300 damage to all enemy units in a large area of effect. Nuke a base's defenses and all of them create Broodlings to attack what's left. Granted Apocalypse has a huge cooldown of several minutes, but one use is usually going to be enough.
As in Wings of Liberty, the campaign involves a lot of tech and upgrades that aren't present in multiplayer, and they snap the game's difficulty over their leg like a twig.
Zerglings can be upgraded into Raptors, which have cliff-jumping, leap at targets to attack similar to Charge, and have a +2 damage buff, or Swarmlings, which mutate 3 from an egg and only take a couple seconds to mutate. And by the way, Swarmlings can still mutate into Banelings. And speaking of Banelings, they can be upgraded too. Hunters are cliff-jumpers and leap at targets just like Raptors, or Splitters leave to smaller Banelings when they explode for further damage. You can also give Banelings innate upgrades to heal nearby Zerg on eruption, or increase their black radius by 50%. A perfectly viable strategy is to just mass Swarmlings, mutate them all into Banelings, and move them through the enemy's base, blowing up anything they roll past as the enemy kills them.
Roaches can be upgraded to have a slow-on-hit effect like the Marauder, better than the Marauder in fact, or to spawn Roachlings when a unit they've attacked recently dies. Roachlings are basically Zerglings, and they spawn two at a time from any enemy killed after being hit by a Roach.
Mutalisks can be upgraded to have their glaive worms bounce three more times, hitting a total of six targets, or to give up the bounce entirely for a +9 damage buff to armored targets. Or they can get a rapid bonus to HP regen rate when out of combat. Because ya know, Mutalisk swarms weren't deadly enough already, they need to tear through targets even faster, or hit and run more often thanks to better health regen.
Swarm Queens. Their Heal ability is autocast compared to the normal Queen, and they move faster off of creep. The result is similar to the idea of taking a Hydralisk and giving it the Medic's heal ability.
Aberrations can now walk over smaller units like the Colossus, and have a powerful damage buff against armored enemies like the Immortal. Your main opponents for the campaign is the Terran Dominion. Marine, Reaper, Ghost; those are the units that aren't of the Armored type. Everything else is going to be shredded. In the same vein for defense are Impalers, Lurker variants that have 9 range and tear through Armored enemies almost as good as the Aberration.
Ultralisks can be upgraded to revive upon death with nothing needed for it to happen but a 60 second cooldown on a second revival, or to release noxious clouds of gas to damage enemies further. Even without those two evolutions, they can get Burrow Charge, which is like the Zealot's Charge but they burrow to do it and stun enemies when they erupt. Ya know how the biggest problem with the Ultralisk was getting them close to the target and not stuck behind your other troops? Not a problem anymore.
Heart of the Swarm introduced the Terran Warhound, which was intended to be an Anti-Vehicle unit; however, it was removed on the basis of it being this trope — a powerful Lightning Bruiser whom very few units were cost-effective against.
Harsher in Hindsight: Zagara states how she feels sorry for the Terrans because they don't have a hive mind, and therefore are each alone. In Legacy of the Void one of the first things the Protoss are forced to do is sever themselves from the Khala so as to be free from Amon controlling them. Afterwards each one states how alone they feel now they are no longer connected to one another.
In Wings of Liberty, Raynor said to Orlan he ought to kill him when he'd captured him after trying to sell him out to the Dominion, but he might need to hire him someday, and hands him over to Mira as a prisoner. This time around, Orlan is hired to hack the Dominion network to find out where Raynor is imprisoned, after the Raiders fight Mira to free him.
Also in Wings, UNN's Donny Vermillion once accused Raynor of allying with the zerg to overthrow the Emperor, which is exactly what he did in the final mission.
A more minor example with the Hellion. One of the unit's Stop Poking Me! quotes has him say "Like a bat out of..." before stopping. In Heart of the Swarm, it gets a new form called the Hellbat.
Seeing Zurvan. When you are trying to wake him up by feeding him, with what you see of him, the player would guess he's some Sarlac thing. When he wakes up, turns out all you were seeing was his mouth—he's huge.
The mission chain where Kerrigan infiltrates the Dominion science labs. Stukov is back, he's infested again, Narud is Duran, the Dominion has been helping him create Hybrids, he's working for Amon, he's a shapeshifter, the Tal'Darim are his servants.
The final mission. You're not facing the standard terran fare, you're facing the mercenary upgrades of them. Things get really heated when the Prides of Augustgrad shows up, which are a pair of Jackson's Revenge (or improved versions of the Loki) Battlecruisers. And these things respawn. And if that wasn't enough for you, make it to Mengsk's base or wait 22 minutes and the Odin reappear. You know, that war machine you had in the last campaign that mopped the floor with the dominion defense force?
Inferred Holocaust: Kerrigan routinely is contacted by broodmothers wishing to rejoin the Swarm, and Kerrigan tells them the price of admission is to infest a world. The evolution missions also take place on planets you don't visit in normal missions, but are in the process of being invaded by another brood mother. All of the planets targeted are military strong points, but it's unclear whether they also have civilian populations.
Just because she's reformed doesn't mean Kerrigan hasn't lost her touch. To destroy a protoss shuttle out of her range, she implants a broodmother larvae into a captive protoss, then lets them warp her on-board, sneaking the larvae on. The larvae then consumes the captive scientific specimens on the ship to mature, hatch a brood, and systematically destroy and infest the ship.
Duran/Narud manipulated the Dominion, UED, the Protoss, the Zerg, and the leaders of the four factions, all towards a plan to create the Hybrid and revive Amon while marginalizing potential threats like Kerrigan.
Valerian when he takes the throne at the end of Heart. Most of Arcturus' loyalists are probably dead or dropped favor with him due to Raynor's exposé in Wings, he has good publicity with the people for helping to evacuate them during the invasion, he's personal friends with Raynor's Raiders (and with them probably has more support in the outer worlds than Arcturus) which means he also has a possible line to the protoss, and he's on good terms with Kerrigan. He's not only taken control of the Dominion and proven his cunning and intelligence, but his position is more secure than his father's ever was.
Memetic Molester: Abathur wants a sample of Kerrigan's essence. Not helped by the fact it's revealed he was the one who put her in the chrysalis that first turned her into the Queen of Blades.
Just in case there was still doubt about Mengsk being a bigger asshole than Kerrigan is in her current state, he proves it to us again in the opening cinematic when he has his forces keep firing on the Hyperion even though Valerian, his own son, is onboard it, and Mengsk knows that. The saddest part is that Valerian is not surprised about it.
"My father is willing to sacrifice any piece on the chessboard, so long as he takes the queen."
The Zerg, particularly Abathur and the Primal Zerg, are obsessed with "essence" to the point of Cargo Ship. It's a play on their "purity of essence", and it's made clear that the term is used for genetic sequences that could strengthen them if assimilated. Still, "we must absorb their essence" and the many permutations of the phrase sound silly, and after you hear the word repeated over and over and over until the end of the campaign, it will likely just sound sillier each time. It gets worse with Dehaka, who apparently based every one of his responses around the words "essence" and "collect". The writers were apparently aware of this, since some parts (including the argument between Dehaka and Zagara) play it for laughs. They'd initially planned for the sequences on Zerus to be much longer, and the Primal Zerg's evolution through essence to be more prominent. Since ultimately Zerus only got a handful of missions, they had to stress the point through dialogue.
The Tal'darim are back, and just like in Wings of Liberty, they are so over-the-top in how OUTRAGED they are by you even daring to approach their sacred artifact it can easily appear as comical.
See the building that enables Swarm Host? One of the unit-enabled icon in it looks like Scaredy-shroom. It doesn't help that Swarm Hosts are shrooms-on-four-legs.
Zeratul putting his hand over Kerrigan's face and saying "BELIIIIIIEVE" as he gives her a vision of Zerus.
As Famous Last Words go, "Ah made you into a mawnster, Kerrigan" aren't exactly in the top ten.
Offscreen Moment of Awesome: Jim Raynor's fight with Nova. We only see the set-up, and all we know about the aftermath is that they both survived, but its safe to assume the entire facility was destroyed.
One-Scene Wonder: The game makes a big thing about spawning a new brood mother named Niadra and giving her the objective to destroy the Protoss, but she is abandoned on-board a derelict Protoss vessel with her brood after just one mission. Not seen again since.
Nova, seen only in the second mission before disappearing for the rest of the campaign. However there will be an expansion pack based around her.
Padding: "With Friends Like These." Matt and Valerian contact Mira Han to get Colonel Orlan, but she refuses to hand him over because she held onto him for Raynor, and a mercenary has nothing if not her word. The thing is, they want Orlan because they want him to hack the Dominion base to find out where Raynor is being held prisoner. Not to mention Matt is her husband, and he and Valerian are still currently in control of Raynor's men. Yet, she refuses, and thus Matt resorts to shooting his way through dozens of her mercenaries and destroying her bases to make her yield. Valerian even lampshades they could just talk all this over, but it's like someone tossed your opponent a three-way Villain Ball, Conflict Ball and Idiot Ball, because their actions make absolutely no sense. But, if they just listened to reason, there'd be no mission.
The entire mission is Played for Laughs, with characters constantly lampshading the insanity of the entire situation and generally acting a lot more lightheartedly than they normally would. This is, quite likely, not by mistake: the mission both follows and precedes incredibly dramatic, intense, emotionally draining gameplay sequences. In a situation like this, comic relief is exactly what a player would need to let off tension. It also helps that the mission has a unique, almost arcade-like, quite easy gameplay compared to nearly any other level in the series. Basically, it's an opportunity to sit back, take a breath and have a good chuckle before watching Jim losing his faith in Kerrigan on-board the Moros.
Player Punch: The final Char mission is an exercise in this, since the goal is to kill the Four-Star Badass / Reasonable Authority Figure who helped make Kerrigan human again in the previous game, gained Raynor's trust and respect, does his best to evacuate civilians and wounded from the Zerg onslaught. Most of his lines are What the Hell, Hero? which Kerrigan doesn't have an answer to.
Romantic Plot Tumor: Many fans believe the romantic plot between Jim Raynor and Kerrigan is this because they feel the romance is forced and takes away meaning from the plot of the first game, despite justifications from the story author. The other half of the audience are begging Blizzard on their forums to give Jim and Kerrigan a happy ending in Legacy of The Void. But since that expansion is supposed to be centered on the Protoss (and because of the dislike of their romance mentioned earlier) this leaves the first half of the audience to fear their romance is taking over the plot.
Ron the Death Eater: Kerrigan; while there is no question that a lot of her actions are questionable in the game, and there are indeed many people amongst fans who tend to overlook this, just as many people tend to insist she doesn't deserve redemption for her past actions. Nevermind the fact it's made very clear she was not fully in control of her actions as the Queen of Blades and genuinely feels guilt for it.
Scrappy Mechanic: Blizzard introduced MMR decay, which makes players start from lower divisions based on how active they are. For example, if you are in Masters but don't play any games for a month or two, you can find yourself bumped down to Silver. This has led to situations were extremely skilled Masters level players are getting bumped down to the lesser skilled divisions, resulting in a lot of Curbstomp Battles. It's also disheartening for people who are used to being in higher levels then being crushed by other people used to being in higher levels, especially if they come back and don't know what MMR decay is. To sum it up, they are low level players upset because they are being crushed, there are high level players coming in who are disheartened for ending up in lower levels then normal, and there high level players who are being bored or feel bad about crushing players who are way less experienced than them.
Stop Helping Me!: The game feels more "hand-holdy" than previous installments. New abilities given to characters will be the only solution to the current situation when the ability is introduced, which, while obvious enough in and of itself, is accompanied by someone pointing out exactly this: "Use this button to solve the problem!"
The campaign starts off with several tutorial-like levels. In addition, the protagonist will lean on the fourth wall a bit to nudge the player (though without What the Hell, Player?, more like "For your information player"—such as "Hey, I should use X ability right now"). Finally, the interface now contains more direct hints ("Move hero here," "Click the Mutate Structure button"). This "assistance" persists into at least the second-highest ("Select only if you are a StarCraft veteran") difficulty level.
Izsha will inform you it takes three Drones to mine Vespene at maximum efficiency right up to the final mission, and if you put off going for an optional objective, she pops in to remind you about them.
Izsha's recommendation to make Zerg Units that can attack flying units will pop up on a frequent basis towards the end of the game, too.
Two different versions of the GUI used to give orders to units now exist. One is the "standard" array of buttons (at least six commands for any combat unit) while the "Simple" version offers "Move," "Attack" and special ability sections, excluding items such as Patrol or Hold Position.
Strawman Has a Point: Kerrigan already dances on the edges of being a Villain Protagonist, then comes this exchange. Arcturus's words do not change the fact he had a major hand in Kerrigan's rebirth as the Queen of Blades and the creation of the Hybrids, but his rebuttals to her are a bit more convincing than hers to his:
He gets another one when he points out that she pissed all over Raynor's efforts to save her, and that he'd probably loathe her. Kerrigan's reaction is subtle but its there.
That One Achievement: A good portion of the Mastery Achievements can be considered this as most of them require the player to finish the level in a ridiculously short period of time, not only forcing the player to act quickly, but allows for almost no room for error.
Of the Mastery Achievements, there's a particularly large player agreement that "Premature Evacuation" for the Rendezvous mission is the most annoying of the lot; having to destroy ALL the Dominion structures before the Zerg reinforcements arrive after a 15 minute time-frame...with nothing but Zerglings, Queens and, at this point in the game, a fairly weak Kerrigan hero-unit.
That One Level: On Brutal, The Crucible is this, a Zerg version of Wings of Liberty's turtling mission, All-In, to protect a giant chrysalis. Hardly a surprise either, since it's the one Heart of the Swarm mission where you don't have an overpowered hero unit at your disposal. (Unless you don't count Niadra)
There's something endearing about young Broodmother Niadra and the way she tries her best to grow up... even if her 'doing best' means being a Xenomorph-expy.
The first time Broodmother Zagara meets Kerrigan in the leviathan, she is doing a certain Victorian gesture of respect, in which one lifts one's own gown a tiny bit while bowing. She continues being Kerrigan's posse through the game.
The broken-tusked Zerg that's always near Kerrigan in cutscenes near the start of the game, her interactions with it come across as being a bit like a dog and its master.
Years ago, a cinematic was leaked depicting the hypothetical end of Heart of the Swarm. And when the game was finally released... that scene was recycled and used again, albeit with a few tweaks. Those tweaks really change the meaning of the ending though, despite some scenes having been reused.
It didn't take long after the first game to figure out that Emil Narud was Samir Duran. Some fans speculated though that they may have been rivals working against each other, or they were actually different characters. Turns out no, they were right all along. And even though they never outright state it in Heart, Legacy has Zeratul spell it out.
The Woobie: Raynor keeps being this. At least half of his effort from Wings of Liberty are seemingly completely destroyed by the beginning of this game.
Iron Woobie: Stukov; after getting killed by Duran and having his whole faction killed by the original Queen of Blade in Brood War (making him a Senseless Sacrifice), then being resurrected as an infested terran and cured, it turns out he has been infested again, as well as kept prisonner and experimented on by Narud for years. He can never goes back on Earth, and if he could, there would be no place for him, since he is half-Terran half-Zerg. Yet, you don't see him mourning about it. He even seemed a little excited about possibly fighting "a good death" against Amon, since he has no other purpose left in life.
Jerkass Woobie: Kerrigan, big time. She has barely recovered from being Brainwashed and Crazy into acting like an Omnicidal Maniac for entire years, and shit just start being thrown at her again: Mensgk keeps wanting her dead, her boyfriend is apparently killed, and when it turns out he is alive, he is so horrified by what she has done to herself that he doesn't want anything to do with her anymore until the finale. Any wonder she is so pissed off?