Thanks for your feedback.
Correct, if you have Flash enabled you will get the old version (not responsive, fancier more colorful UI).
If you do not have flash, or it is blocked, as it is on all mobile devices and all browsers now by default including Chrome, you will get the HTML5 version.
The version you are most likely referring to is HTML5 and built for mobile-compatibility first and foremost. We tend to err on the side of simplicity and usability for this version over design aspects during this phase of the app’s development so that it can fit in with almost any website and work well on any device. The design is purposefully minimal for usability purposes and also to allow the design itself to have the majority of the focus and color in the experience.
We are able to do custom skins for the HTML5 app on a custom project basis, if you have a specific look and a development budget we can accommodate some UI changes.
We are improving the HTML5 customizer on a regular basis and you can expect a lot of great updates in the next months and thru 2018.