I guess I just don't think much of it at all. Probably in the minority with that opinion, though, based on some of the responses.
I used to think it wasn't anything special. I tried playing it a bit on my own and it seemed very basic. What was the point of doing anything? I think I'd seen so many imitators nothing it did seemed all that special. It kinda felt like the Seinfield effect. Where a younger person might go back and watch it and not think it's funny because all the jokes have been ripped off to death since.
It wasn't until some friends dragged me into it, and I started with a few small goals, that slowly it sunk its teeth into me, that I started to realize how smartly designed it was. There is a reason it is so popular. It is incredibly deep with a good learning curve. It's designed to encourage your creativity, even if it has to coax it out of you, you boring adult (like me), over time.
We once had an amazing experience where one of our friends got separated from us by thousands of blocks in the Nether via a rare bug no one seems to have heard of. I realize that bug obviously wasn't intended, but it lead to something that sort of was, a crazy wild expedition through the Nether to save him (The nether is the underworld of minecraft, and you go there via a portal. Every one block you go in the nether equals 8 blocks in the above world. So two portals 100 blocks apart equals 800 blocks in the main world). The adventure to save him that ensued was unlike any other I have ever experienced. Three of us suiting up and traversing this wild untamed wilderness, truly a wilderness that no human hand designed, having to make our way through was absolutely exhilarating and I will always remember it. This experience couldn't be created if it was a human crafted world. But the algorithm minecraft uses is so expertly designed, it never feels off or procedurally generated. And again, that's not all of the game. The game is built within that world and tailored to making sure your experience in that world is fun.
At the end, we not only rescued him, but we found he had gotten somehow stuck in the biggest Nether fortress we'd ever seen. We looted the place, and all of us headed back, finding some new pathways that would lead the way for a literal highway between where we'd started and this far far off nether fortress. Eventually my buddy built a massive ice highway, which you could apparently travel via boat and traverse in less than a minute. We went to the overworld at the fortress and the above ground had a fantastic area with a lot of resources we didn't have easy access at home. So then we started working out a little system of getting things back and forth. The building of that system was so much fun. Everyone contributed different things to make it happen.
It was just such a wonderful adventure. No other game really provides that. Minecraft is designed to ensure that your time in that world is fun and engaging. It gives you systems that are easy to get into and are well balanced to ensure you always have something to pursue. You can set up a basic goal, starting small, and the game will help make that goal happen, while gently nudging you towards grander ones. It is a huge rabbit hole to get into.
Most survival games I personally do not find fun at all. They are always very one note and always very limited. To me the "depth" doesn't feel intuitive at all. They're also pains in the ass. And a lot of procedural games are just empty slates. A lot of pointlessness. A lot of dead ends. Their systems usually end up feeling convoluted and arbitrary. They're always full of a lot of dumb bullshit. They always need constant updates to be fun and not get boring right away. But when you look at Minecraft, it's so naturally deep and all about overcoming pains in the ass with your own problem solving. It doesn't have any of the dumb bullshit. And it doesn't even need updates to be fun. 1.0 was a lot of fun. The updates just seem like bonuses. Kinda like Tetris.
If you look at the vast swathe of games that try to do things that Minecraft does, whether focusing on one area or trying to imitate it directly, and you see how they fail, then you start to have an appreciation for the fact that Minecraft makes it feel so effortless. That takes real skill, and there's a reason it resonates with so many people.
Sometimes something is super popular because it's like potato chips, like marvel movies. Low effort, low investment, easy to munch on for fun. Broad surface level appeal. But other times something is super popular because it speaks to something so many people have and so expertly handles it, with a natural depth that appeals to both casual players and to the more hard core players it pulls in, including from the casual side.