Seconding the performance issues. This is obviously amplified when screen sharing, which makes certain types of collaboration difficult. (Remote grooming sessions, for instance.) I also find recent UI changes have made the product harder to use, at least for our version and processes, and have added nothing of value in return.
As far as how useful Jira is, a huge percentage of that is going to be your team's processes external to Jira. I have found it to be a very good mirror. If your team's processes are a mess, your Jira instance will quickly become one as well. But if your team is organized and is bringing an existing, functional system to Jira, I have found that it's a good enough value add to be worth it.
It's definitely an enabler, though, rather than a tool that will funnel you into good practices. (The same can be said for Confluence but it's even more true there IMO.)
As far as how useful Jira is, a huge percentage of that is going to be your team's processes external to Jira. I have found it to be a very good mirror. If your team's processes are a mess, your Jira instance will quickly become one as well. But if your team is organized and is bringing an existing, functional system to Jira, I have found that it's a good enough value add to be worth it.
It's definitely an enabler, though, rather than a tool that will funnel you into good practices. (The same can be said for Confluence but it's even more true there IMO.)