Hmm, there's many different things that many different people find appealing about this game. And perhaps that's one of its greatest appeals, it has a lot of different things you can do, but aren't really forced into doing anything if you don't want to. So, heading the list, we can put 'player agency'. You do what you want to do in the game, there is no railroad plot forcing you down a particular path. There is a goal laid out with the Community Center, but there are also many ways to go about completing that, including going down the Joja Route if you prefer. And there's nothing in the game forcing you to complete the community center either. The only real timed thing is the return of grandfather's ghost on Spring 1 of the third year, but even that isn't a hard and fast time limit, because you can always put a diamond on his altar and summon him again if you want the reward from his approval.
The next thing that I, personally, find appealing about the game is that most of the NPC's are more than just cardboard cutout stereotypes. Also, the community has more than its fair share of drama that you can uncover as you live in town. This isn't a perfect village with perfect people and perfect motivations. There's drama, there's some very questionable decisions being made, there's scandals. It's a messy, gossipy town, and is more immersive for it.
Pairing with that is the sprite-based graphics. Keep in mind, this was all done by one guy. He doesn't have an AAA budget, so he needed to create a visually appealing game on the cheap. So he went with sprite sheets, and I am absolutely here for it. He could have tried to do some kind of '2.5d' stuff with 3d modeled figures in an isometric view plane, but that would've been much more difficult and, frankly, probably looked worse. He picked an aesthetic, and he ran with it. It's pretty clear he took a lot of inspiration from the SNES era of gaming, and did an (in my opinion) amazing job with it. So I guess you can tack on 'visual appeal' onto the list.
Now let's get into the mechanics you interact with. Ultimately, your character will generally want to make money somehow. There's many ways to do so, depending on which mechanic you wish to interact with. Do you really enjoy the fishing minigame? It's probably the fastest way to make money, bar none, in your first year. So if that's your thing, you can absolutely do that. However, if you don't particularly like the fishing minigame, you don't really have to interact with it much, outside of trying to complete the fishing bundle for the community center if you so decide. Farming is generally the most likely thing for many players to focus on because, well, your character is generally referred to as 'the farmer', so that's kind of a hint. And while fishing can be the most short-term profitable, you can get more long-term profits from farming. However again, you aren't *required* to farm if you don't want to. So in addition to player agency, there's a wide variety of mechanics, and generally most people can find something enjoyable in the game as a result.
Now, for myself, with a background in the financial industry, I found it extremely enjoyable to figure out how to maximize my profits very rapidly. In fact, I've written more than a few guides on that topic. I've done quite a lot of number crunching and calculating to min/max my income. For those who like that sort of thing, this game is amazing. There's several others in the community who have also done independent in-depth examination of profit margins, ROI, and other metrics by which you can measure your profit. And doing so and following these strategies can make a large amount of money. But simply being rich isn't the end-all-be-all in this game. Many things you do in the game don't require much if any money, and you can make a decent amount of money with any number of strategies without ever opening up a spreadsheet. It's something you can do, this isn't EVE Online, you aren't required to use spreadsheets.
So, I suppose that's my answer to your question. Player agency, visual appeal, a broad variety of mechanics that you might 'click' with, and enough depth to 'deep-dive' in full tinfoil-hat mode if you are so inclined, but not requiring diving if you don't want to.