I think nTask is great (especially the business features like the risk management), however the Gantt functionality is not currently as good as some competitor software. I think the following would help a great deal:
Improved task integration - parent tasks inherit dates automatically from sub-tasks. There is a workaround using project dependencies from the first and last task in a path but this is clunky.
Please make the subtask drop down arrow bigger! It is nearly impossible to click first time. Also the drag-and-drop approach to task nesting could be made more intuitive with some clearer animations.
Zooming. Is a vertical zoom possible? Can the UI architecture integrate crtl+scroll or is this browser dependent? What about a little overview pane?
Labels on task bubbles. The % completion is great. Could they have task names next to the bubbles too?