Liège is a highly interactive city with many things to do and see. Below is an outline of when things are open and where they are located. This should help plan your visit and make sure that you get to see everything you want to.
Life can be unfair, and I think Liege (or Lüttich or Luik depending on who you ask) is a good example of that. The city is rather nice. Its not as pretty as Ghent, and its certainly way nicer than Cologne. I would put it on par with Antwerp and Brussels. So why then does nobody go there?