I went for a 3 day break end of Oct 2017. It is not a great City and 3 days was far too long as there is very little to see. Maybe the xmas markets will keep you busier, but once you have seen the old town (which is only 30 years old having been bombed to bits and rebuilt) then you are virtually done, even the old town is a struggle for a full day.

Did manage to see Legia Warsaw while there which was great, but overall a disappointment.

If you want to be impressed for a 3 day break go to Krakow...we went for 3 days oct 2018. More than enough to see, and I would even go back again it was that enjoyable