First and foremost, I love Data Designer. It is easy to use and a great combination of Rules engine and Reporting. The case and formula fields work beautifully.
With that said I found a slight hiccup, that I would love some enhancement on. So currently when you publish a report from data designer it automatically carry over into report builder. However there are some features that are not available in data designer explore that are available in reporter builder. Example Ranking. So now every time I make a change to data designer and then re-publish a report, I also have to remember to go to report builder and redo any additional setting or preferences i.e. Ranking.
I would love to see some additional features that mimic report builder.