Jim answered your Critical or not question.
If you have Update configured to "automatically" download and install you
will get every update critical or not
Change the Update to "notify when available but don't download
This way you get a little message saying updates are available where you can
then go to the Update website using
Internet Explorer an let it scan your system....it will then inform you of
what you "need" and mark them as Critical or otherwise.
You can see them and their descriptions and then decide which ones to
download...critical ones should be.
Software updates for hardware installed should come from the Manufacturer of
the hardware.
peter