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.
Crack Pairing: Michael and Zara, for rather obvious reasons: One's a twenty-something male human living on 21st century Earth, the other's a century-and-a-half-old Eldar Farseer who's only a couple of inches tall. It's saying something when the Rose of Slaanesh thinks that it's really strange that the two are a pair.
Crazy Awesome: The united 'Order' forces getting their act together in Chapter 19, and kicking serious ass.
Crowning Moment of Funny: Zara finds out about loli's after Michael complains about the Emperor's trolling him like a character from a Japanese porn game. Turns out even the Emperor'sonly found out about that stuff recently.
Even the Emperor of Mankind is made Fun Size in this setting!
Why do the 40K characters occasionally spout pop culture shout outs (particularly egregious with Porthos the Grey Knight? Because they are assimilating modern (ancient) society; quirks, references and all.
Mary Sue: Averted, as the only reason Michael is in this story is because of his Blessed with Suck powers of Weirdness Magnetism providing the Warp Gate that put them there as a 'path of least resistance'. Plus, the reason he's able to keep several BadassArmies from killing each other and him? Part of the Super Power Lottery winnings was that he is able to manipulate people's perceptions. On the normal scale between humans, this means he's mildly charismatic to negate his shyness. On the mini scale, he could convince Space Marinesconvinces ORKS to cease fire.
Plus, the guy has taken a lot of injuries and has (almost) never been on the winning end of a serious battle. The slapstick violence between him and the minis, however, is about even and what you'd expect from a comedy.
Nightmare Fuel: Long after he has killed his first daemon, Michael still choked up in fear whenever he so much as thought about them. Of course, this leads to...
Nightmare Retardant: Apparently, the sight of daemons literally vaporizing from being shot up by a literal wall of Gatling guns works well for this.
No Yay: During Chapter 25, the Rose of Slaanesh's...relationship with Michael becomes more and more disturbing, and it becomes exceedingly clear what kind of a relationship Michael would have withher.
Shipping: Quite a bit of the fan following ships Michael/Zara, Meliya/Sohm and Amadeus/Samisha. Guarantees this, too, since there isn't much in the way of romantic competition (yet) and their real problem is that their partner might die in combat, as none of them are non-combatants.