What makes Dragon Quest fun? Not a set up, I’ve never played one
Traditional. Some find this bad. I find it a blessing. Dragon Quest is the anti-Final Fantasy. You know how in FF they scrap EVERYTHING every single game no matter how good the ideas were? They never used X-2's battle system EVER AGAIN despite how awesome it was. Or X's. Or XII's. Every entry has an emphasis on trying to innovate and switch things up to the point where it often feels unnecessary. DQ is not like this. Every game builds upon the one before it. It is highly iterative and features, rather than being nixed entirely, are often taken and improved. For example DQVIII ps2 had an alchemy feature but it had an in-game timer. You'd literally have to wait to finish an item. Well, in IX they took this and made it instant. What this means is that DQ has been doing this for 30 years. What you essentially have is 30 years of traditional rpg perfection. Comfort food is a good comparison. It's basically grandma perfecting that recipe she's done for 30-40 years. Yeah, there's newer dishes available, but no one can cook that one dish as well as grandma. They've perfected a formula.
Personally, I fount XI fucked with that formula and changes too many things but since you are a new player this won't mean shit to you.
While it's not known for it, it also has great storytelling. In DQIV, you play multiple chapters as different party members on their part of the world and then in the final chapter you all meet up and form a party. No one attempted to make an rpg story like that before DQIV. Multiple jrpgs since have tried to copy it, from SaGa games to Suikoden III. Dragon Quest V features one of the most unique narratives in gaming: the story of a boy who grows into a man, gets married, has kids. DQ games often have a vignette story method where stories within the game are often self contained. This makes it perfect for casual play. You can start a town's story, beat it, take a break, and after the break continue to the next town and start an entirely new story. DQ stories are also often handled in very detailed ways despite their simplicity. In DQVII for instance you find a village over filled with poison and every thing - man, woman, dog, cat - has been turned to stone. You're too late and you couldn't save them. On your journey you find more villages with stoned people and you're left with trying to wonder what happened. DQ tends to take a more subtle approach to its storytelling than other jrpgs which are more in your face.
This is less the case in XI because it has far more cutscenes than any other DQ to date and has a more modern in your face jrpg ethos but for a new DQ player it might still feel refreshing.
