Sorry for the long and sort of disorganized wall of text. I was thinking through trying to add some more advanced stuff as a mod, realized I didn’t have anywhere to put it or a reason to use it, and then that turned into this post on progression.
TL;DR: Cataclysm’s only optional difficult areas with unique stuff available are labs. I’d like to see more of that added, potentially in a couple of different layers, to draw out the end game and make the pre/post lab transition less stark.
There are (more or less) four different progression systems in Cataclysm (skills, gear, CBMs, and mutations), which I think is really cool. They also all interact with each other (you need skills to craft high-tier gear, for example), but they aren’t tightly coupled - you don’t need all of your skills to be high to get more mutations or CBMs. That seems like it means that there is a lot of opportunity to make some really interesting progression and a lot of interesting character builds. There’s also the process at the beginning of the game where you need to get a steady supply of food, clean water, and now heat, but I’m leaving that out here because it’s very much a thing for the early game and it (more or less) gates the rest of it: If you don’t have food, you don’t have the time to craft gear, raise skills, or refine a mutation set.
Speaking of gating, one of the problems I have with Cataclysm’s progression is that there isn’t very much area gating - there are very few areas that you want to reach, but need to be properly prepared to get there without dying. Two examples come to mind: One is Acid Ant nests, which you need good acid protection to get near but you may want to, because of biosilicified chitin’s properties. The other is Labs, which require computers and a way to deal with robots, but reward CBMs, mutations, advanced skillbooks, and a bunch of late-game equipment. There are certainly other difficult areas (Fungals, Triffids, city centers, etc.), but there isn’t really a reason to go there.
We do have plenty of tough monsters - masters, hulks, top-end robots, triffid queens, etc. Those are all dangerous, even to late-game players (though most of them can just be sniped at range if they don’t surprise the player or happen in a confined area like a lab), but with a few exceptions they don’t really give any sort of reward or reason to engage them. A hulk in a city could mean you need to kill it to get to a gun store, but you could go around. Or kite it off. Or find another gun store. Bio-op zombies seem to be the exception here, since they are the source for high-end CBMs.
The progression systems are also uneven: top-tier melee gear and armor is crafted or found in relatively safe locations like museums or mansions, top-tier ranged gear is in bunkers or (again) labs. Skills are mostly gated behind books - a character can book-learn to 4 cutting, 3 dodge, and 3 melee, and that will keep you mostly alive (especially if you also have book-learned tailoring and fabrication). Books can easily be found in safeish locations, and the time to read them is tied to having a food and water surplus, something that most characters establish in the first few days. Mutations and CBMs are both mostly gated behind labs - mutations because mutagen doesn’t really spawns outside them, CBMs because while you can get CBMs pre-lab it’s likely that you’ll have an easier time getting a few levels into a lab to find an autodoc than clearing a hospital. I think that all of that ends up feeding strongly into people’s ideas of early, mid, and late game: Early game is when you are limited in the area you can move in (due to lack of food, water, vehicle, etc.), mid game is when you can move freely enough to find everything you need to get to labs, and late game is after you’ve done a lab (or three, since the challenge doesn’t really vary except in ice labs).
So, labs end up as the only place with challenging enemies that contain things that make you want to go into them anyway, but once you do that there aren’t many other challenges, both because you have everything you want and because you’re at top-tier everything and things that aren’t automatic gunfire or fire can be shrugged off. That ends up limiting voluntary progression, since once you decide you’re ready for a new level of challenge there’s only really one place to go. I’d like to see more progression opportunities added, places that mean that a (current) end-game survivor feels like an early-game survivor who lucked into a kevlar vest and a combat knife in a military surplus store - not a helpless shower victim, but not an unstoppable post-human death machine who can beat a hulk to death with the corpse of another hulk. And, like an early game survivor with a combat knife, see a clear opportunity to start rectifying that - there’s a bookstore over there, there’s a gun store that can be accessed soon, and raiding that museum might help gear up.
There is some of this happening with mods - PK’s adds hell towers and cathedrals, which serve nicely as sources for the marine items and have lots of fire-based enemies. Ascension (though I haven’t played with it) promises to give reasons to go fight the triffids and fungus. Certainly, reasons to fight the triffids, fungus, blob pits, and city centers seem like a good starting point. Thematically crafting materials seem like a good way since it’s unlikely that the various invading forces have much that’s directly useful - what if, for example, survivor gear required mi-go leather, or if there was useful (not necessarily better, but with unique and helpful abilities) gear that could be crafted with fungal tower or triffid heart leftovers. Maybe fungal fireproof clothing or something. Integrating with the crafting systems seems like a good way to make sure it’s gated behind both skill (requiring fab 9+, for example) and ability (you need to be decently advanced to kill a triffid heart), as well as sidestepping the issues around how a lone survivor could craft something superior to what was available pre-cataclysm.
Things like triffid groves work well for this, since players have to choose to enter them, and that means that they can contain threats that are challenging to the current end-game survivor (and which will potentially inescapably destroy low-skill characters) - anyone who is there decided they were ready, they didn’t open their shelter door to see a skeletal juggernaut across the street. Labs finales (potentially even multiple danger classes of labs, like ice labs or labs filled with mutants and/or heavier robots) seem like a good place to put any of the tech stuff, potentially including tools required to work with the new materials (like the wrench and the welder, but for monster-based equipment!). Portals (both the ‘natural’ ones that happen randomly and the ones at the bottoms of labs) also seem like a good place to put this sort of end-game stuff, since who knows what’s behind them, and again it’s the sort of place that a player has to choose to enter - if you’re going to create a monster that requires a full loadout of end-game gear to deal with, it’s not going to be fun for early or mid game characters to encounter it.