Improve the navigation.
It took me a long time to figure out how your current navigation works. It would be better if there was a direct link from one tutorial to the next one, and probably to the previous one and the "parent" as well.
R Long commented
Agreed. This might seem like a trivial thing, but when one is somewhat uncertain about properly approaching complex subject matter, clicking "Back" on the browser and selecting something gives the distinct sense one might not be doing the tutorials "properly". I mention this as a professional developer of 20+ years, though one completely new to XNA. If I'm perceiving the continuity value of this kind of "handholding", I suspect less-experienced or new developers would as well.