People over on the invite-only beta of Bluesky (not sure how many users, but still a very small amount) are nice, happy, and excited about how interesting and open it is. Like Mastodon, it's an early decentralized social network (not compatible with the fediverse and like, with only one instance so far).
Unlike Mastodon, it has much better UX, and people are very excited about getting to have good timeline algorithms that they themselves have control over. (I haven't done a scientific poll or anything, but my guess is most people online prefer algorithms to show them stuff they might miss vs. sequential timelines.)
Everyone agrees Twitter is terrible now, but there's definitely a lot of people who haven't made the jump to Mastodon. I think Bluesky might end up attracting a lot of the people who are turned off by Mastodon being way too confusing and unfamiliar.