Developers accustomed to QlikView have lamented the lack of customization with the Qlik Sense interface. I don't entirely disagree with them, but think there are a lot of compelling reasons to use Qlik Sense other than how it looks. I wrote some of them up here a few years ago, and that was referring to a much older version than is available now.
However, to make Qlik Sense look better, out of the box (no extensions), I recommend making good use of text objects and concentrating on the use of color in the design.
Here's an example of one text object from the What's New in Qlik Sense February 2019 demo app (yes, those are hyperlinks):
The nice thing about themes is that they are deployed in the same way as extensions, so updates to the theme automatically roll through to every app using the theme. This is preferable administration, maintenance, and (likely) performance over the centralizing of default colors in QlikView done by mature customers. I haven't seen themes embraced by a large number of customers yet, and I think it is a missed opportunity.
If you're still feeling nostalgic for QlikView, Barry created a theme with the QlikView default color palette (as well as Tableau and Power BI look-alikes):
However, to make Qlik Sense look better, out of the box (no extensions), I recommend making good use of text objects and concentrating on the use of color in the design.
Text objects
Text objects are significantly more customizable than what was available in QlikView, with different formatting, sizes, etc. and any number of expressions, all within the same object.Here's an example of one text object from the What's New in Qlik Sense February 2019 demo app (yes, those are hyperlinks):
Colors, themes
I don't think the current, default Qlik Sense color palette is great, which is a good excuse to look into themes. You can generate a theme using your company colors, in addition to other default differences in appearance your developers prefer, using a free theme generator like https://sensetheme.com/. Developers who are comfortable with CSS can go beyond even that. The most important thing to focus on in your theme is the main few colors used for series in graphical charts, i.e. the colors of bars, lines, and symbols.The nice thing about themes is that they are deployed in the same way as extensions, so updates to the theme automatically roll through to every app using the theme. This is preferable administration, maintenance, and (likely) performance over the centralizing of default colors in QlikView done by mature customers. I haven't seen themes embraced by a large number of customers yet, and I think it is a missed opportunity.
If you're still feeling nostalgic for QlikView, Barry created a theme with the QlikView default color palette (as well as Tableau and Power BI look-alikes):