Just started playing last night after watching several hours of videos. What a terrific, engaging game!
Most of the ideas posted here have to do with gameplay, but I have a few suggestions for the interface itself.
First of all, it's really, REALLY hard to see weapons and other items that have been dropped. Some sort of graphical element - a dashed border, or occasional "blink" perhaps - would alert you to the fact that there is something with which your colonists can interact.
Secondly, it can get really challenging to keep up with all of your colonists. At times, when they occupy the same space, it's difficult to select one instead of the other. I would like to see a panel that lists each colonist and their current tasks, perhaps even their health status. Clicking on a name will center the character on the screen and select them. This could even be built into the existing Overview pane.
EDIT: A similar panel would be useful for buildings and equipment. I would like to see a list of elements that need to be repaired/cleaned, and a list of equipment that can be toggled. For instance, if I am running short on power, I can go into this panel and click all interior lights to "off." Again, clicking on an item name will center it in the view, so if there's something on fire I can find it right away.