I haven't been to Hamburg since 1991, when I was 9, so I may not know exactly what to do for an older person, but here goes: When I was there the DOM was in town, that was a huge festival, I think it's more of a late summer through Ocktoberfest thing (I was there the entire month of August, 1991), again, I was 9, but I knew what was up, every german beer you could imagine and I'll bet lots of ladies. Also, since my mother is devoutly Catholic, she took me and my brother (who was 11) to church. It just so happened that the church was smack dab in the middle of the Reeperbahn (St. Pauli's), or the red light district... bet you could have a ton of fun there 😛. As far as eating goes make sure you check out the Blockhaus (sp?). It's a chain steakhouse that was really good. I'm sure there are a few i'm forgetting If i reemmber ill let you know.
We did some trips, like Bremen for the day. I had just read the Bremen Town Musicians (Remember I was 9) so I was all psyched for the town, but I'm not too sure how great that could be if I were older. A great city to check out if you love history is Lubeck. It was a main city of the hanseatic league (trading dynasty that lasted from ~ 1200-1600 if i remember correctly) some really great history there. We went to Berlin (via the IC, I bet you could swing the ICE which is really quick) for the usual, Brandenberg Gates, Reichstag, etc. and then we went to Copenhagen and checked out Tivoli. It was a really great trip, and I could imagine I'd like it 100x more if I were 23, which reminds me, maybe my next vacation could be there! If you need anything or have any questions, PM me, my dad has been to Hamburg (for work) at least 25 times and knows the city really well. Have fun man!