What's great
I like Metabase, we've used it in the company I worked at for a while, and as a BI analyst I get most of my day-to-day tasks done there. As a non-technical user it saves lots of time as I don't rely on devs for SQL and tasks that would otherwise take much time (e.g. visualization), are done quicker. It is also great for cross-departmental communication.
What needs improvement
Despite its growth and (I would assume) huge budgets going into understanding what their customers really want, the exporting dashboards and their customization elements are very hard to navigate. What I mean is that, just like everything else is optimized for simplicity, so should data visualization be as well. Perhaps a tool that you can have a look at that does a great job and is similar to Metabase is TalkBI. You simply click on one button and poof - report is made. Other than that, perhaps it would be possible to review the SQL generated by Metabase so we can help improve its effectiveness for more complex queries.