UH was tough for me to get to replay. I thought it was mainly due to the snark of the main character, as well as Ged, the person encouraging you to act so everything doesn't go down the drain. Ged cusses sometimes. A few cuss words are nothing in the face of mass extinction, I got it, or I thought I did. This doesn't change how I enjoyed the meat of the game, or what I thought. The most amusing parts to me weren't the direct jokes but when the game stood back and let me think about things. Okay, yeah, I could pull back from the game any time, because I am a person with free will, and the game is just an HTML file with graphics and sound. But the pacing was organized well enough that you'd have a hub and branches, and the hub was pretty clearly a Good Place to Sit and Think of Things. Perhaps UH was too heavy on snark at times, which is okay. But it didn't rely on snark. It did other things to establish a Futuristic Tone, like having about/credits explicitly listed metadata. So I knew what I was getting into. But on reflection, I saw a theme of loss throughout the game, of worlds we dreamed up and let die, and how having someone in our created world keep it alive is, of course, an extreme exception.
You start out on Mars. Humans have moved here long ago, leaving behind a doomed Earth. There are pyramids of information, some practical and some not, and you've been chosen, for whatever reason, to look into them and find something. You're given a multiple-choice quiz you can cheat on, with easy undos, and it seems it's more of a way to catch you-the-player up on what's happening. Often, only one or two choices aren't ridiculous. The quiz to some extent establishes a theme: with all that technology, the witty repartee feels mechanical (responding "was that the first question?" to "Are you ready for the quiz?" is an example.) This pops up later, when you start analyzing the best social responses in a situation, ones most people would quickly choose either way, e.g. polite white lies or overbearing, overstated truth.
Because, as you find out, you're in a simulation. In fact, you are in U9, a very deep simulation, below U8 and so on. So it makes sense that, that far away from humanity, some of your emotions become quantified to some degree, and natural actions, such as deciding whether to tell your friend they look great or awful, become rigorous show-your-work-a-thons. I think it's no mistake that there is no real humor from your point of view, no "oh, that's neat because X," only comebacks.
After a few more evaluations, you find out you may be able to astral-project, and you find your quest. Your world is likely to be deleted. Nobody uses the information from your world any more or cares. Besides, you wouldn't understand stuff like soccer. You just wouldn't. Trust me, the overseeing computer says. It's not worth asking about. You've had a good run, no offense, but it takes work to upkeep, and you do understand your own self-interest may be adjusting your calculations? You and Ged both, really. Ged particularly adamant things should be saved. He provides actual reasons.
If you accept the challenge, you're sent forward into the real world (U0 or U1–I forget) to take a box with your world in it away from the people who are about to destroy it. Even if you succeed, things are irrevocably changed. You probably don't want to go back. And sort of like Narnia, the time you spent away is nothing compared to how time passed below, but unlike Narnia, there are no allegories or talking animals or aesthetic places to explore or wonder. Because, well, simulations are a dime-a-dozen. And I think UH meant not to give too many details, because it wanted to emphasize that even people in badly created or imagined worlds have a world and belong there, and it's the only one they've got. The semi-random, deliberately imperfect, odd graphics seem to reinforce this.
I think I got tripped up on some terminology and some science-fiction conventions, and when I kind of rolled my eyes at the swearing and snark, it probably cost me some Comprehension Points. So I didn't get as much out of this as I could. But there were still more than enough takeaways. The erasure scenes are very good, if you tell Ged to get lost. Given your character's snarky contrarian bent, it feels a little dirty of the game not to give you the chance, or force you to undo a lot. I'd have appreciated, once the game was over, a way to revisit the critical checkpoints and branches to see what happened if I messed up elsewhere. And certainly the whole "we're in a simulation" thing reminds me of all the times I played a game to somewhat-lose to see what was going on. All the people I killed with my decisions, this time through, all the simulations I aborted because I wasn't interested, with no Ged to save things remotely! Even the worlds I created in my head, whether with Legos or a computer program (e.g. The Sims) or even purely mentally, I imagine them drying up and sort of hoping they could save themselves somehow--of course nobody in there has free will or emotions--but I'd like them to live on. While UH kind of crushed me with all the mental worlds I'd created and left behind to shrivel, it also provided a story as to how they could keep going. So it was more to me than standard OMG YOU'RE IN A SIMULATION.