I stayed at the 'Europäischer Hof' with my sister and her 6 years old son for three nights and we definitely enjoyed our stay.
The room and bathroom were well-sized, but maybe a little stiff and not very cozy. The breakfast and other food facilities were excellent. And the staff were very helpful in giving us recommendations on what to do and where to go.
The recreational facilities were formidable: a swimming pool, the longest water slide I've ever seen, a huge sauna area with different types of sauna, squash courts etc. Since these facilities are only available to hotel guests they are not crowded at all and very clean.
We also appreciated very much that, for the first 3 days of your stay, your room card is valid as a ticket for the underground, city buses, etc. It also includes a free harbour cruise.

the standard rooms are ok (103EUR). Nice carpets, medium sized rooms, bath room not too small, but not very cosy....staff is a little arrogant, without credit card (mine was stolen when I was forced to spent a night there) you are obliged to pay the room in advance. NOT WORTH YOUR MONEY AT ALL. Rooms are all very noisy, environment round the hotel is full of prostitutes, drug dealers....railway station is very close.

And the best thing was:
3 weeks later I received a letter, they told me to pay my phone bill. I NEVER DID A PHONE CALL IN THIS HOTEL. They sent me a piece of paper that states, that a phone call was made from hotel room x at date y. I was in room x, but at date z, not at date y. I tried to tell them, but they did not understand, that I was not anymore in Hamburg at the time, when the phone call was made. They want me the pay the bill of some other guy! Unbelievable for me! So make your own decision whether you want to go to this hotel.