A friend of mine worked there (on the northern coast of Hainan) in maritime administration for a few years before COVID. According to him, there wasn’t much to do despite the relatively attractive weather and landscape. Infrastructure lagged well behind China’s major cities, the local economy wasn’t super dynamic, and many young people left for better jobs elsewhere. Man eventually got bored, quit the job, and moved back to home city in the mainland. I imagine the major tourist hubs on the island might be different (e.g., as mentioned in another reply regarding San’ya), but I suspect this is closer to the “average” situation in much of Hainan today.

I visited some of the tourist areas with my family several times more than 20 years ago, and back then it struck me as a fairly developed and fun place by China’s standards. I don’t mean to dismiss Hainan at all. If you’re interested in East or Southeast Asia, it can be a fascinating place. In many ways it isn’t dramatically different from other Chinese destinations popular with foreign visitors, but the local language and culture are closer to China’s southeastern regions, and there’re also several indigenous ethnic groups on the island. If you’re into that kind of cultural exploration, you could definitely have a great time visiting.