Yes, absolutely. In my opinion one of the nicest German cities. Don't miss the little ferry boat (public transport, hence included in HVV tickets) departing from Landungsbrücken, e.g. to Finkenwerder. See http://www.hadag.de/e_hafenfaehren.php

Also, in case you haven't heard of it, check http://www.miniatur-wunderland.com/. Be careful, it is really easy to spend countless hours in there and miss everything else.

Other than that I guess there is quite good information on the web and lists for "what to do with one day in Hamburg" - if you have any further questions feel free to ask.