Improve the "Describe Field" functionality by including some visual analysis (especially a histogram), to offer a quick analysis about an attribute, such as min/max range, histogram, number of unique values, standard deviation, ... Quick mockup shown below based on the "country" attribute of the superstore dataset.
When exploring a new dataset, one of the things I most frequently do is creating a quick histogram on an attribute to figure out how it behaves inside the dataset. Creating a histogram and counting possible values is not difficult to do in Tableau, but when you have to do this for 20+ fields it gets tedious to do this over and over again. The current "describe field" functionality goes in the right direction but stays too basic and is, ironically for Tableau, too much text to really be used for data exploration. Would be great if "describe field" would be extended with basic visualizations.
Cherry on the cake: Would be great if there would then be a way to convert this standard quick analysis into an out-of-the-box dashboard for us to further play with (hence the "Explore" button in the mockup below, which would create a dashboard showing exactly what is shown in the "Describe field" box and put it in the users hands to take it from there).