I loved the several days I spent in Hamburg a couple of years ago. Mainly I went for Minatur Wunderland but the whole city was awesome. Very laid back. Beautiful people.
I booked my MW ticket in advance online. In the summer they are open until 23:00 so I went in the evening. It wasn't very busy at that time. I think I got there around 18:30 and stayed 3.5 or 4 hours. It was still twilight when I left but it was early July so the sun sets late that time of year.
I enjoyed the city hall tour. And the Hanburg city museum was also very good.
I booked my stay through the Hamburg tourist bureau website so I got a room upgrade, 3 day Hamburg card and some other perks. Stayed at the Sofitel which was awesome.
I agree that the city is very walkable. The whole inner Alster area is nice. The public transit is also fantastic of course. In the end I was surprised how much I really enjoyed my time there. I would love to go back some time. My Germany trip report below starts with Hamburg