No, I'm not talking about any incarnation of Warhammer as an expert or even an informed noob. As much as I *may* know about Warhammer, there are people who have lived and breathed either all of Warhammer or some particular variant for long enough to pick anything I say apart. So I'm not even going to pretend special knowledge. In fact, other than knowing what Warhammer 40,000 was; I never had any interest until a few years ago. And as far as enjoying the core dynamic, tabletop war-gaming aspect, it's not gone well. A few years back I got keenly interested, bought an Adepta Sororitas box set that was getting harder to find but was still reasonably available (I bought it off of eBay from Britain, something nearly impossible at the moment) and one of my kids got a Space Wolves box. And then a new version of Warhammer 40k was released that changed the rules, and according to some people made both box sets at least half-pointless.
We still have the boxes. I like building models and have never gotten in to miniatures-building, so that's a possibility. Except every time I think I've got a grasp on how to paint miniatures I come across another video that does things exactly the opposite and claims it's the best way to paint. And fundamentally, my inherent OCD conflicts with, as far as I can gather, a fundamental conceit of Warhammer 40K: it's not meant to be taken seriously AT ALL.
Warhammer started out as Warhammer Fantasy Battle in 1983. It was a miniatures tabletop war-gaming system, such as had been popular for a while. This was the same concept that informed Dungeons & Dragons. Except while D&D increasingly embraced
Warhammer did something different: it was the first (successful, anyway) war-gaming system built around ITS OWN MODELS. Now, I've tried to figure out how this worked. Because technically you could STILL use whatever miniature models you wanted. Right? But I have certainly formed the impression that this is frowned on by the majority of the Warhammer community and is almost entirely forbidden in community tournaments. And absolutely forbidden in "official" games, which is a real thing that the creator, Games Workshop, does. While I can see how "official" rules would forbid using "non-official" merchandise or rule-sets, I have a hard time understanding how this has expanded throughout the Warhammer fandom. It's so pervasive that, as I mentioned, when the two boxes of miniatures we had that were published under, IIRC; 8th Edition rules were not included in 9th Edition rules, there was a pretty consistent dialogue that they were useless unless a named unit was specifically included, which could also happen with future rules updates.
But anyway, the point of all that is to say that Games Workshop based Warhammer Fantasy Battle on proprietary models, AND made it STICK. To the extent that the various versions of Warhammer to this day use constantly changing model sets as the basis of their business plan. The single most common complaint I have seen about Warhammer is that GW hasn't updated a particular faction in a while, which seems to put said faction at a disadvantage. I suppose this is a form of nerfing, then. After all, if one particular faction has been updated with a new rule set, but another is/was built for an older rule-set and is just being incorporated into the new system, their specific battle rules may not take proper advantage of the new system. I suppose. Games Workshop tried to change things up a few years ago by ending the Warhammer game and replacing it with "Age of Sigmar," which to me is similarly-themed but of course requires all new miniatures and uses many new factions and rules. This apparently didn't last long, as the original setting has just been re-released as "Old World." Except using new miniatures and new rules.
I don't actually know as much about those settings as I do Warhammer 40,000, which was launched in 1987. I guess because I was much more into tabletop games by then (mostly Star Wars The Roleplaying Game by West End Games) I was aware of 40K in ways I never was with the first game. 40K takes the same ethos as Warhammer but moves it into the 41st Millennium, with lore to explain how humans got from Warhammer in the fantasy past to Warhammer 40K in the far future. Are any of these ideas original? Ehhhhh...not many. Maybe not any of them. Even the original game sourced a lot of lore from easily-identifiable or generic sources. The thing Warhammer had conceptually was this "grim, dark, crapsack world." In my opinion, Warhammer 40K amped this up with the move to a new setting. I kind of wonder if that was the point, really. You think REALITY sucks? Come play this game where being alive is nothing but pain. And that's from the humans' point-of-view. You could also play as ancient alien robots. Sure, that sounds cool but you have no soul. No identity. No thought. Oh, you USED to be an individual, but your king stole all your souls and made you all robots to win a war against gods. No, that was actually maybe a good thing because you all had SUPER CANCER and lived in constant pain and knowing you were gonna die Real Soon Now. Or you can play as this other alien race that's super cool but you don't hardly ever reproduce and you're kind of easy to kill except for the super-powerful leaders AND YOUR GOD IS GONNA EAT YOU WHEN YOU DIE. So don't do that, in this galaxy designed specifically to kill you as quickly as possible.
Everybody is psychic, unless you're not, or one of the really weird ones who are ANTI-PSYCHIC. There is one major faction that has very few overtly psychic individuals, but everybody kind of believes the same basic concepts, and their thoughts are so simple and direct that the collective psychic force of their belief can OVERCOME PHYSICS regularly. The humans have a faction with a similar ability, although more focused and situational. I mentioned early on I had an Adepta Sororitas box, and one of the things that faction is known for is such astounding, deep, and abiding faith in the idea that the Emperor of Mankind IS ACTUALLY AN OMNIPRESENT GOD they can manifest miracles.
But that's not to say gods aren't real. They are. And The Emperor of Mankind *may* actually be a god. Or he may be dead. It could go either way. Hyperspace in Warhammer 40K is the flip-side of the universe that enables faster-than-light travel. At least for some factions. Except it's not just hyperspace, it's literally hell. I mean, a version of it, anyway. That's where all psychic energy comes from, and it's where the actual gods are. There are a few big gods, and probably many little gods. That we know of, anyway. The easiest to understand is Khorne, the Blood God. If you've ever heard or read "Blood for the Blood God," that's a reference to Khorne. Similarly Nurgle is also well-known; the God of Disease. You'll see allusions to Nurgle in many properties. Less-known are Slaanesh, a young god spontaneously created about 10,000 years prior to the "current events" of Warhammer 40K. Basically the space elves were so good at being the best at everything, they were increasingly focused on extreme pleasure, obsession, and achieving just to achieve...which created a god. Unintentionally, but still. Hardest to understand is Tzeentch, the God of Change, who technically kind of fills in in between the boundaries of the other gods, but is also the primary user of sorcery; as magic such as this is pure chaotic change. There is technically a 5th Chaos God called Malice, but you have to be pretty dedicated to a specific idea to make sense of this god. So I'm just going to mention it and move on.
There are other gods, both racial and historical. Their reality and impact on the ongoing galaxy is taken very seriously by some and ignored by others. The Orks, for example; have two gods that seem to exist solely to start a fight. Which I'm sure they're thrilled about, if they know.
The Orks may be the poster-child for "you're not meant to take it seriously." They're not dumb, but they do limit their thoughts to only a few things. Orks grow until something kills them, so the bigger an Ork is, the older they are, AND more important. Because if you're bigger, you're probably more adept at killing things smaller than you. Orks are practically infinite and reproduce through spores, being intelligent, bi-pedal, humanoid fungi. Which means that any planet an Ork has been on just has Orks now, and always will. Unless you THOROUGHLY burn the ENTIRE PLANET. Which almost every other faction in the game *can do,* but the people who CAN do it have to KNOW about it, and the galaxy is big enough that that doesn't happen much. The Orks, along with almost every other faction, can legitimately claim they will inevitably win the galaxy. But the Necrons can say that, too (the race of robot people I mentioned). So can the Tyranids (an extra-galactic threat somewhat like the "bugs" from Starship Troopers. In fact, the more intelligent and technologically-accomplished your faction is, the more you are aware you're *probably not* making it out of this setting alive in the end. On the other hand, maybe you are the only way to survive.
But as I pointed out, even though you CAN take it seriously; I really don't think you're meant to. It's an absurd setting where absurd things happen. But it also doesn't really matter. If you find a faction you like, and some stories you like, you can play the game however you want and IT DOESN'T MATTER. In the end, really; the only ones getting in the way of the fun seem to be...Game Workshop.