Project Zomboid is the closest we're ever going to get to UO2. It is simple, isometric, immersive, and brutally punishing. You grind up skills and (can) die in one hit. There are writable books and nestable bags. It too is "a game for people who like collecting things".
It is the manifestation of the transience I always talk about. Perhaps stop by our server and see how you like it.
Project Zomboid has solved an age-old problem. In many shooting games, there is an extra melee button for quickly smashing nerds that get too close. However, it's usually just some damage and you only really use it for combos. PZ goes a step further and adds a general purpose "push" button that is available, whether you're meleeing, shooting, or unarmed. For downed opponents, this same button stomps on them. It's such a simple feature but it really goes a long way in both making the combat immersive and maintaining a good flow of options.
One of my greatest joys in games is collecting random garbage and using it to decorate my house. PZ allows us to pick up pretty much any object and then place it down somewhere else. This leads to a very fun minigame of not only decorating a nice base, but going out of your way to collect rare objects. Cosmetic progression is the only progression anyone cares about.
In Project Zomboid, there are many ways to die. You can bleed out, food poisoning, zombie virus, burn to death, starve, or even freeze to death. However, what I love about is not that there are so many ways to fail but that each and every one only happens due to your negligence.
You walk faster than zombies. You'll only get bit if you get greedy or complacent. You'll only get life-threatening injuries by crashing cars or jumping off stuff. Almost never is a death not directly your fault. The first 30 hours might be learning the many ways to die, but the next 300 are intelligently choosing when to risk it for the biscuit.
When you do finally die, your character wanders around as a zombie with all your things in their inventory. The main thing that you lose is skill levels. You can then make another character and go get that stuff, although I prefer to just start a new world entirely. It can feel a little cheesey after five characters have inched their way towards a base.
This game punishes your mistakes but does not abuse you.
One of the more unusual design choices for the game is that every action takes time. Moving an item into or out of a bag takes time. Placing objects on tables takes time. Equipping things, investigating things, reading books, and even eating food takes time.
The amazing benefit of this isn't really felt until you're under siege by a horde of zombies. In those tense moments, it matters so much how you organized your items and which traits you took at character creation. It matters which weapons are on your belt, on a table, or in a box in the next room. It is one of many small mechanics that compound to create a truly immersive, spatially-reasoned experience. Only Ultima Online has given me this in the past. That feeling is my favorite thing in all of gaming.
If you do not get a good night's rest (quality bed, enough time, well fed), you will awaken in a mostly normal state. However, you will get tired earlier on the next day or possibly have neck pain. This makes it harder to both be productive and to get a good night's rest the next night. Just like real life. You have to take an intentional action to break the cycle or these small hiccups will pile up and crush you.
No one factor in Zomboid will generally turn into a game-ender. It is fun and immersive to plan your exercise soreness around your sleep schedule or be reminded that you slept in a chair. Embrace the moodles and they will embrace you.