So, I've finished retribution in three campaigns, plus nearly finished eldar.
Overview:
The campaign is really blatantly the space marine campaign with the player race swapped out. As previously mentioned, the Tyranids get it the worst, what with two missions set on a planet the Hive Lord should not give the slightest fuck about, and barely rates the attention of some bullshit non-sentient hive tyrant, on account of it being entirely full of ice, old buildings, and people with guns. There are also two missions on a different low-biomass planet, but there is an actual reason that time. With everyone else, it's just slightly grating that you never fight imperial loyalists, and the dialogue sometimes doesn't quite make sense.
Ironically, the biggest plothole is in the IG campaign, where a major plot event could apparently have been negated by the Inquisitor calling up someone.
Races:
Imperial Guard: You have the Lord General Castor (who is a jerk), who favors the sniper rifle and can call in aerial reinforcements, plus he leads a small squad and gives guardsmen squads additional dudes and other bonuses. Next is Inquisitor How-The-Fuck-Do-You-Spell-That, who is intended as a melee combat monster but falls flat due to lacking sufficient health and attack speed, though she does have some pretty impressive pysker abilities as she levels up. Sergent Major Merrick is Heavy Weapons Guy, being basically Avitus except shittier. Still, he's reasonably useful once he's taken his time setting up. There is also the Commissar, who can shoot people to inspire them, plus he's decent at Melee. As you might expect, the IG revolves around outnumbering absolutely everyone and Leman Russ support. You have squads that are not basic guardsmen, but eh. There is also a Baneblade.
Eldar: You have Kaelyth, who wrecks people's shit at whatever range you designate by basically being an Exarch for every Aspect Shrine at once (Okay, so the backstory is probably more complicated). Ronhan is a ranger, who is good for sniping fools. Veldoran is a warlock who has a bunch of blasty powers, and there is a Farseer whose name I cannot recall who does healing, some buffing, and sitting on the ship crying because the Wraithlord you can deploy with instead is a fucking wraithlord. I may be confusing her and Veldoran on that point, but i'm pretty sure he's the Seer Council. I used guardians, banshees, and the occasional Wraithguard, which was possibly less than optimal. It is possible to straight-up
miss the Avatar.
Chaos: Eliphas continues to affront Grandfather Nurgle. He can be specced as dedicated to any chaos god except Slannesh. All of them alter what shrines built on the battlefield by heretics and what worshiping heretics do. Notably, Khornite shrines summon daemons who die after a short while, which leads into the hilarious exploit that completely wrecks the difficulty of the rest of the game once you do it. Neroth is a chaos sorcerer who can do blasting, other types of blasting, and varied forms of daemon summoning, which also feed into aforementioned exploit, especially the one that requires you to sacrifice a unit (Not a daemon, the developers are not quite that stupid). Prior to that, you leave him behind for a dreadnought. Kain is an aspiring champion, who you leave behind because he makes Havocs more awesome by not being there, or give plague cloud and a melee weapon to assist the next dude. Varius is the bringer of the hilarious exploit, because he's a plague marine who, in order, raises everyone he personally kills as plague zombies, raises all dead friendly infantry as plague zombies, and raises everyone who dies as plague zombies. Since Daemons count as infantry, you can bury everyone beneath an endless tide of zombies, daemons, and zombie daemons. You can also sacrifice zombies to Khorne to summon more daemons, who then become zombies. I pretty much just used Chaos Space Marines, Havocs, and heritics (for shrine building), even before Varius got his top-level zombie powers.
Tyranids: You have the Hive Lord, who is a sentient Hive Tyrant. He can summon squads of new Tyranids to the battlefield for free, but they consume popcap. Instead of other heros, you get starting units; unlike the honor guard units of the other races, they consume popcap. All of it, if you make the mistake of getting access to high-end 'nids. If you unlock all unit types, you get to have a popcap of 54/60 and a maximum of 10 dudes. If you deliberately cripple your army diversity because you love seeing Gaunts tear shit up, you get to discover that they're horrible at intermingling squads, which is a problem for obvious reasons. The super unit is the Swarmlord, who is another Hive Tyrant, but instead of scything claws and possibly a ranged weapon he has four arms. With swords instead of hands. It made the endgame mission mildly hilarious, because the end villain kept gloating, and I was like, "Dude, you have two
named Tyranids after you, you're kind of fucked."
Mechanics: You get refunded their cost when units die, which should probably have been mentioned during the tutorial mission. Or, you know, at all. It means the IG gets infinity resources when using massed infantry and reinforcing via the Lord General.
Sniper weapons no longer cause suppression apparently because fuck Cyrus. Or possibly bugs. The ingame tips state that they do, but the in game tips are full of shit on that point.
There's this really irritating tendancy towards hard railroading, where areas simply aren't places you get to use abilities at until you do whatever the game wants you to.
Plot:
Okay, so it's been a decade since the end of Chaos Rising, during which time Kyras has been summoning daemons on every planet in the sector. The IG got sent in on a massive scale, which led to having a shitload of traitor guardsmen as well as the blood ravens turning to chaos. The Imperium responded by shipping in a bunch of Cadians, many of whom turned traitor too. Oh, and some Tyranids are still alive. Plus, Eliphas is back.
So, for pretty obvious reasons the Inquisition says "Fuck this" and pronounces Exterminatus on the entire sector. <Player Faction> discovers this after killing <Leader of other faction> on Typhon, and have to break through to an interplanetary teleporter/warp rift/digestion pool to go to Caldaris and protect a town under attack by Traitor Ravens, or straight-up kill them and incidentally protect the town. The Hive Lord then goes and kills some orcs, while everyone else has the option of doing that, but the next plot mission is destroying a warp portal on Aurelia, which for some inexplicable reason is also a planet you want to protect from Exterminatus, despite it being made of ice and cultists. The Hive Lord goes to Aurelia after defeating the orcs for
no goddamn reason.
Next up is a raid on Capital Spire, which a Cadian traitor regiment has recently conquered and is expecting a call from the Lord Ascendant, Kyras. The player race intercepts the transmission (even if they're Tyranids) and tracks Kyras to Typhon, then get in a fight with the Eldar, who are trying to stop the Exterminatus fleet from arriving. Note that the player Eldar do that as well. With the Eldar dead, the Exterminatus fleet arrives and bombards the planet while the player makes a mad dash for their exit.
The player ends up on the Judgment of Carrion, and have to defeat an ork Mek who is even crazier than usual, except for the Tyranids, who fight a whole bunch of other Tyranids while an Alpha Zoanthrope reestablishes the Hive Mind across the subsector. Also, the player race figures out that Kyras is sacrificing the entire subsector population to Khorne.
Next up is Cyrene, where the player fights traitor guardsmen, Alpha Legion, and Traitor Ravens, then goes and kills Kyras.
Racial Endings:
Tyranids: You call in the entire Hive Fleet. Imperial causalities are 98% before they manage to escape. This includes the Exterminatus fleet.
Chaos: YOU sacrifice the subsector population to Khorne
IG: You manage to call off the Exterminatus fleet.
.