I really like being able to create emails like newsletters in NXT, but the design features are very limited. One feature I would like to see is the ability to add a shaded background to an individual section. The only option I can find now are is to shade the entire body of the email. We're trying to move from Constant Contact to NXT, but the styling features are just not there yet.
I'd add to this, the sizing of content blocks and font options available. Both are limiting factors on our adoption of NXT email.