That's a little difficult to list, really; a lot of "settings" are fairly generic (going too far down part of the formula below), and some comparable settings I've not looked into enough (e.g. Infinity).
For me, I like Last Days: Zombie Apocalypse and Frostgrave as more "modern" (in terms of release) skirmish game settings; LD:ZA could easily be replaced by Mantic's Walking Dead games as "Zombie Apocalypse Skirmish", however, which is partly why I can't compare them to Necromunda.
A lot of what makes "Necromunda" a great setting is because it's a
named "Sci-Fi Wild West Frontier", setting which got bought into as a
name, as well as pretty much the first of it's kind, in an ecosystem of games where such a game did not exist (you could argue that Rogue Trader had the initial skirmish level, but it didn't have the overall setting fleshed out)
.
For actual "Wild West", there was once a Necromunda rewrite to use the rules in the Wild West, but I fail to recall what its name was - it was fairly generic as it was a simple rules rewrite. Since then, you have Wild West Exodus, which I understand is a slightly larger scale in terms of model count, and Dracula's America, as well as some of the nameless Historical systems I've never really looked into, but they don't really properly push a grungy sci-fi angle.
For Sci-Fi, you have Mantic's Deadzone and Infinity, but neither really push the lawless frontier angle. Simply put, Necromunda had a unique angle between genres that helped it to stand out, even at a time when there weren't really any competitors.
If you were to step into an alternate reality where Necromunda wasn't released back in the day and release Necromunda now - take the name away, take away the history that's built up with it - and it suddenly has a lot more work to put in against it's competitors, and it would get compared to whatever would have been created first in that universe in (primarily) the Sci-Fi genre.
I think parts of the formula (if I knew the whole formula, I'd be writing a setting and rules system to sell and swim in the resulting money) are (certainly helped by):
- Having a pre-existing universe for people to step into as a hook.
- 40k in Necromunda's case. Mordheim came along and lived in WHFB, and as with Necromunda had fan-created alternative campaign settings.
- Gorkamorka also had 40k, but removed too much of where it came from as to not really hook people; there was no thread linking them to the larger universe. Things happened on Necromunda and could influence the Imperium; Things happened on Angelis, and people would still be doing what they'd always been doing.
- Alternatives at Mantic have named planets/countries, but most systems are "setting agnostic", which can be a double edged sword.
- Stepping in, but not too far.
- Outline one aspect of the game setting [Hive Primus, how it works in general and the gangs that live there], have other places existing in a vague way, but don't stop allowing for players to make what they want (the contents of Hive Secundus, for example, were never really elaborated on, and multiple hives exist but are never even named).
- Necromunda fleshed out some names of places and vaguely what their environment was, but they didn't forcibly tell you that place A was located at B, C distance from D, had large battle cannons and macro batteries from downed space ships and was definitely permanently controlled by person E. You had the flavour, but could pick and choose how that went together.
- Which, as a contrary example, is a turn-off for me in N##, which goes into so much detail for the entirety of the planet, the government, how houses work etc. as to alienate my private headcanon.
- Having a setting that allows for variety and variation.
- You can have multiple different House gangs, for example, but the "duplicate" House gangs can be armed in varying ways. You can have outlander gangs, and duplicates can be equipped completely differently.
- Even if you have similar gangs and loadouts, you're morally flexible within the story of the game/campaign to do different things and create different story arcs.
- This is probably applicable to any game, though; Blood Angels, Dark Angels, Imperial Fists... Inquisition using xenos weaponry versus hating all xenos...
- Having a setting that gives people a twist on what they know, so they can still use what they have.
- 40k is big battles - Necromunda is grungy scraps for survival, but they're mostly using the same weapons and equipment. Both can have fights in hive cities, and locations within the hive can be varied enough to fit "other places" (terrain), but provide a different sensation. That weird alien planet tree = that weird hive fungus.
- Having a system people can pick up easily; either be familiar to your player base, or be simple.
- Necromunda used the (at the time) familiar 2nd ed 40k rules with some tweaks and new campaign/progression/"rpg-lite" rules, so the potential/target player base would more likely be familiar with the structure of the gameplay. (Some Osprey-based titles use similar systems to retain some level of familiarity for their potential player base).
- The rules of the time being similar to the larger 40k system allowed for cross-over; you had alien stats in the back of the Big Yellow book to include Genestealers, Orks, Eldar, Loyalist/Choas Space Marines etc. which allowed for more people to buy in from the larger 40k community, which allowed for a twist on what they knew (see above).
- The current system of N## throws me for a loop, as I don't get its complexities and variations (even within itself, therefore *not simple*) compared to the original ruleset.
- For an example of simple systems, Frostgrave uses D20s with reasonably simple modifiers to calculate close combat/ranged combat/magic; showing someone how the system works wouldn't take long, and "complicated" situations are easy to intuit from the pre-existing examples. From what I can tell, Frostgrave is popular in part because it is relatively easy to pick up and play. Rangers of Shadow Deep varies on this ruleset with different scenario mechanics to provide a different gameplay experience, but is familiar for those who have played Frostgrave to not be a leap.
- Pushing the game and letting people know about it.
- Games Workshop have (or had, probably still do have) the most global reach in the "hobby", with stores everywhere, shouting about their games and blasting it out of White Dwarf in what appeared to be every single possible place you could sell magazines. Back in the day, when the internet wasn't really the thing it is now, that was how you slapped nerds in the face with your product. Most other games of the time would be in the specialist publications and offered by "smaller" companies, most of which wouldn't be anywhere near as well known, and probably forgotten about most of the time.
- It's also why all the alternatives popped up when Specialist Games got neutered back in the day and White Dwarf devolved into a trashy catalogue; people stopped hearing about Necromunda, got turned away from GW stores when they wanted to play Necromunda, so started looking for alternative games and alternative publications (which were coincidentally full of new alternative games).
- The internet being a thing now, it is significantly easier to find blogs (BoLS, OnTableTop), video channels (YouTube, Twitch etc) and webstores pushing a new setting/system/rules/miniatures.
- Getting a big enough player base for the game to support itself.
- Following on from point 6, really; die-hard fans will find some way to keep playing the game if the player base drops off (Hey, you lovely people!); you get enough people invested in it first, though, to establish those fans.
- Keeping the game alive and fresh, but not too fresh.
- This is how original Necromunda (et al from Specialist Games) took a bullet; GW didn't keep it alive and forcibly killed it (not allowing it in stores, not publicising it, destroying stock after trying to clearance sale it away).
- N## is... Fresh?... Every time it releases a book or a sprue...?
- Frostgrave has a second edition, has rules revisions for existing content, and new content on the way as of time of writing.
1-5 have the setting with the rules mixed in; 6-8 highlight that a setting is only as good as the real world environment it is placed in and how it is treated.
I'd think it is possible to replicate the magic, as long as it isn't specifically "Necromunda" magic. It may have even already happened, but no-one knows about it yet.
When the Specialist Games stopped being supported by GW, a whole load of alternate systems sprung up to try and take the place of the various systems, hence Mantic coming to the fore as a miniature provider with their own line of sci-fi and fantasy games, hence Infinity being a thing, hence all the third-party mini producers etc.
Unfortunately, I'd not know much about other sci-fi settings, as I'm pretty much bought in to Necromunda of old, and while I'd happily tout some alternative systems from Osprey, those systems have fairly generic settings, and I'm not aware of people having enough interest to consider them.
For example, there are a few Frostgrave players on here (me being a prospective one), and I'm always happy to wax lyrical about LD:ZA, which has an interesting survivor group creation "mechanic" (you have three types of survivor that you have to pick from as a leader; Selfless, Selfish, and Trained. The selected type can be up to 100% of your group, 50% can be of the Neutral type (dogs, kids etc.) and up to 25% can be from the other type, so i.e. in a Selfish group of 8 models only 2 can be Selfless or Trained, or one of each).
See? I'm off on a tangent because I like how the system (both as a one-off game and as a campaign) works, but the setting is "zombie apocalypse, survive", you'd be making the setting up yourself - while everyone gets "zombie apocalypse", people get "Walking Dead" even more, as more people can orient themselves to Rick, Carl, Michonne and all the various other characters and locations that are already in existence. Given that the Walking Dead games by Mantic also have "generic" surivivor rules, to make your own characters, allows for the separate story of "your survivors" in a pre-existing universe, in turn making it eminently more relatable, more google-able, and potentially more successful than LD:ZA (I've not done a comparison, just going off my own expectations of human behaviour).
There's also recent books like Zona Alfa, Rogue Stars etc. that I'd be happy to go into as potential campaign games, but since they're not as well known or talked about as GW games in my circle of awareness I really don't know how interested people are in them.
I'd even be interested in some pirate skirmish games, but that's a bit of a stretch for me right now - the only reason I'm aware of/interested in them is because I needed to buy a boat for TribeMeet. Even then, I'm not a history buff, and especially not a pirate history buff. I've not looked at buying rules or minis, but those I've seen do pique my interest.
Part of GW doing N## and so on is to try and recapture the magic they threw away, only for it to be picked up and ran with by other people.
...
That's my two cents, anyway.
TL;DR - a setting will do well when they're a twist on something familiar that pushes a new boundary, setting up just enough for a person to flesh out the story in their own head, supported by simple to understand and use systems and are well supported and publicised by their creators.