It's limited to flat files, so you have to plan ahead on what data you'll explore. In terms of the viz - feature parity, but not quite the same at all if you want to do exploration. Which is too bad, because Tableau's ease of exploration is what makes it so much more valuable than PowerBI or custom d3.
What is it lacking in terms of exploration? I thought most of the exploratory benefits were in the visualizations, unless you mean the ability to ad-hoc connect to random databases and begin exploration (because you have to plan ahead to extract flat files from those sources)
I mean in terms of learning to use the exploratory/dashboarding functionality - it's fairly easy to do that with Tableau Public and public data sources (or your own if you are fine with the saved dashboards being accessible to the public).
