Spent a few minutes playing with the map editor, deliberately *not* looking at any documentation:
(First off: no markdown support in the forum software? For shame.)
+ Generally: too many simple icons in use without visible text. This is common in mobile apps, but in a full screen desktop app it would be nice to have some context. The "Turn Order" window is particularly bad: all you see is the token artwork to identify the combatants. What happens if you reuse artwork for 13 mooks?
+ Do tokens really not have "names"? I can't find a way to label one "Orc 1" or "Vole d'Morte" or whatever.
+ Zoom doesn't seem to work. I get the rollover menu when my mouse hovers over the hourglass, but clicking on it just flashes a box on the screen (presumably the menu?) that then vanishes.
+ More broadly: zoom via menu is a bad UI. Pinch zoom is obviously the gold standard, but this isn't a touchscreen app. Zoom via scroll wheel a-la Google Maps is still much better though. Alternatively a grabbable animated handle would be nice.
+ The top level frame has a horizontal scrollbar that doesn't go away (and looks *really* confusing next to the horizontal scroll bar for the map).
+ More broadly again: split horizontal and vertical scroll bars for a 2D area are a poor UI. Again, look to Google Maps, which does "grab and drag" very intuitively.
+ Drawing a "freeform" shape lacks control over the fill color like drawing rectangles does.
+ I can't figure out how to delete objects I've drawn. The "Delete" key, standard in desktop apps, doesn't work.
+ The corner radius control on rectangles is cute, but very confusing. Also: I'm at a total loss for what I'd use that for.
+ The "measure" tool appears to be reporting the maximum of the horizontal and vertical displacement. This is the 4e D&D distance metric, not the 3e one which uses the "every other diagonal costs two" rule. Since you're striving to be system-independent, maybe either delete this tool or have report a true cartesian distance?
+ Pulling down the "pages" menu from the top works well enough (though the icon is IMHO a little confusing).