Well, in order to really get down to why I'm so pissed at it all I need to go into the preconceptions I had about it and which I think most people will have. By the time you're about to descend down there you've played a significant portion of the game so your preconceptions are most likely going to fall into either of two camps. Either you think that the Deep Caverns is going to be the third half of the game, that it is going to be a significant portion of the game and that it will contain a lot of stuff for you to do. Or you're going to think that this is the end-stage of the game, by now the main quest will be far more important and there will be less sidequests as the game's story will move at a momentum to come to a close. I guess a third preconception would be that you think it'll just be a quick trip down there.
So, both of the two former preconceptions are wrong and correct. The third one is wrong.
The Deep Caverns is big, it is huge, it will demand a lot of hours poured into it, so that's why the first preconception is correct. However, it is not a new area on par with previous areas like SGS, Junkyard or Core City or anything like that, instead its focus is primarily the stages of the main quest. So the second preconception is also correct. But that's why they're both wrong as well. In the first one you'd assume that the next area will have characters and quests and a lot of stuff to do and find. However, it is almost barren of those things. If you're hostile with the Tchort and/or the Faceless then there'll barely be anything at all to interact with down there apart from gathing shit and killing enemies ad nauseum(?). And in the second preconception you'd assume that because it is the final stage of the game then the story would be picking up, that now it would be moving faster forward, that it'd be a lot more tight so it could focus on its narrative more than just fucking around.
That's why I find the Deep Caverns as whole to be badly designed. It is trying to be both of those things but at the same time failing at them. If the goal was to make it a big significant portion of the game then guess what? The reason why I enjoyed Underrail was because of its quests, its characters, its factions and dialogue, so a new really big area practically without any of that? How am I supposed to enjoy that? If the goal was to make this purely the end stage of the game and to focus on concluding the storyline then it is shamefully badly designed as it is moving at a snail pace when it can be arsed to move along at all.
Now that's the the big criticism which all others get tied to that make the Deep Caverns unbearable to me. So I'm not complaining about individual things here, I'm complaining about how it all ties together as a whole.
Now then, it's a big area. What's the problem? The problem is that apart from the Tchort base, the starting map where I met Six, the first map to the north of him, possibly some Faceless areas if you've sided with them (I didn't I had to attack them and made them hostile) as well as Leo's place and a few other very smaller locations that are meant to be small hideouts where you can rest and get rid of the Eye Of Tchort debuff; Every single area is trying to kill you constantly and they're filled with elite tier enemies for the most part.
Okay, so it's dangerous, what's the big deal? The big deal is like I said in the previous post; The game does not inform you of how draining the area is so if you go down under-prepared (I was merely moderately prepared and I have like a dozen bandages and a dozen advanced health hypo's left.) then you're pretty much shit out of luck. I said in my edit that I cheated and gave myself unlimited weight capacity and upped all my skills to 130 in order to make the area bearable. Well, after looting a shitload of stuff guess how many advances health hypo's I've been able to craft? 0. Because the gel thingie is nowhere to be found and the trader at the Tchort outpost does not sell it. The area has tons of shit to loot, don't get me wrong about that. And if you're hurting for ammo then there's like 1000 ammo for each ammo type at the eastern warehouse. But just cause it has tons of things to loot does not mean it has 'everything' and even if it does have a lot of stuff it will still be draining you constantly of stuff. And if you don't have a bunch of crafting skills? Well. I'd say you're shit out of luck then because every time you find some grenades you almost immedietly(?) have to use them. So again, bad design. If you're going to force the player to go through a huge area with tons of respawning enemies that are elite tier then you need to tell the player to prepare themselves for it or you need some way to supply the player with shit to use. That doesn't mean I think you should be handed things on a silver platter. Of course not. But the player still needs access to more supplies. The ammo thing can be solved by the warehouse. But healing items? There's too few of them.
So you have to be prepared? Whatever right? Well, even if you do come prepared and go down that elevator with as much shit you can carry without being so encumbered you can't even move there is still more problems. How about the fact that fighting enemies constantly and I mean absolutely constantly gets taxing? How about having to clear out an area over and over again? How about an enemy spawning right after you've killed the last one of the previous batch and need to heal? As much as anyone likes turn-based combat the Deep Caverns is simply relentless. I mean, I can sneak, so like I said, what about those without Stealth as a major skill? It seems like a very biased design decision. Either you need to be a fucking tank of health and damage to make short work of them or you need to stealth around and try to avoid combat like the plague.
Well whatever, you like the combat and with respawning enemies there's just more combat, what's the big deal? Do you enjoy having to backtrack all over the place? Do you like wanting to just go and solve this simple little thing you figured out and having to constantly be barraged with combat? Do you enjoy stealth enemies so good at hiding that they will almost always get first hit? How about that first hit poisoning you like a Crawler? How about the enemy then disappearing like the Crawler? Oh, and by the way, there's usually 3-5 of these enemies around the areas they're in so once you kill one you got to deal with another. You enjoy that? Really?
And while we're on the subject of backtracking, yup, that's right, a looooot of backtracking. And here's the thing, it's not backtracking because I failed to do things in a certain order which could've avoided it, no, the area's locations are designed to force the backtracking. There's a bunch of areas you need to power before you can even get into them. So you need to get to Arke and deal with that place and Arke can just fuck off. Respawning enemies, no hints as to what the hell you're about to do, an AI that locks doors, pours in poison and cold air and fucks your day up. Fuck Arke and Iris the AI. Anyway, you got to go to Arke so you can turn on power and power some places so you can get into them. Except you can't power the Hollow Earth Complex and IIRC the Residential Area at the same time as both consume too much power and you don't have enough to allocate to both. And you 'have' to visit both. So you have to go to Residential, clear it out completely then go back to Arke (enemies will respawn most likely) then turn on power to the other area and then go over there as well.
I'm sorry, but backtracking is good design? No. It is bad design meant to just fluff out the game-time.
The reason why I think the mushroom area and tunnels should be cut is simple: You have to go to both areas to grab an item you need to open a gate to face Tchort. Get it? It's a fetch quest. It's a pointless redundant fetch quest that could be cut completely. The only reason it is there is to force you go to wander around the entire fucking Deep Caverns scavenging for these items.
And here's the kicker, the game doesn't give you any hints as to any of this. There's a thing called "handholding" and that's quite frankly what the Deep Caverns need. Because it appears as if the designers behind it are so afraid of that term that they went as far as they could to the opposite direction and the game suffers for it.
What part of the Deep Caverns is actually good? The aesthetic design is good. The backstory (when you finally get to fucking read it) is interesting. It's challenging and has interesting concepts. But that's about it. The reason why I liked Underrail was because of its quests, characters, dialogue and the knowledge that if I at any point feel overwhelmed I can go back to SGS and wind down by crafting some stuff. The things I liked about Underrail is not in Deep Cavern. If you love the combat and I mean if you get a fat fucking stiffy (that goes for the ladies' nipples as well) when you get forced into more and more and more combat then I'm sure you'll love Deep Cavern.
But personally I think it's just badly designed. It's like a concept artist that sits down to design a power armor and he never stops drawing it so by the time that he does finish it has so much shit on it that it just looks like a mess of details. Maybe they hyped of the Deep Caverns too much and then felt obligated to give it more and more areas while at the same time not considering what to actually 'do' with those areas or how it would feel as a whole.