Liege is far from the crime capital of Europe. I've never had a problem there, though muggings and robberies do occur. Stay sober and stay awake and use common sense. No problem.
If you find Liege to be a dangerous place, you haven't travelled much.
Same here, no problems whatsoever.
One point of interest for me was the stairway of the Montagne de Bueren, 400- something steps there...