Update September 2021
So, this hotel is an institution, especially when you look at the list of previous guests (and their photographs which are proudly displayed on the walls in a room next to the bar, although some of the more notorious ones are missing

), so I booked a room for 1 night, just to see what it's like. As I was there in the middle of the week and on 1 September, the price was reasonable - 140 EUR (incl. breakfast). The prices in the summer are really inflated and whether they are justified is debatable.
The location is great, right on the beach (and a part of it belongs to the Sofitel), the building is really impressive and grand, as are the hallways. Everything exudes luxury... until you get into the room, that is. I was upgraded from a Classic room with a park view and no balcony to a Superior Room with a sea view and a balcony. Hotel_user described it perfectly - it's small and the layout is terrible. The furniture is not my cup of tea either. The balcony is for decorative purposes only, it's very small and you cannot fit a chair onto it, but still it's nice to go out in the morning and breathe in the fresh sea air. And the view is wonderful.
But the biggest disappointment for me is the bed - it's the smallest MyBed I've seen so far. And I don't understand why - there is enough room for a king bed. The same goes for the bathroom. There is room for a bathtub, but there is only a shower. I feel that in such a luxurious and grand hotel a bathtub is a must.
The room was a disappointment.
Breakfast was not impressive either. The offer was very, very limited. All the drinks except water have to be ordered from waiters, which is a drag. No local products, no cakes.
The rest was good. The indoor pool is great and I had it to myself in the morning. The temperature was perfect. The little park in front of the hotel is lovely and well maintained. Welcome drink voucher was good for everything on the drinks menu. Welcome amenity is in the separate thread. I expected more.
Overall, it was good, but I probably wouldn't stay here again when I return (and I will because Sopot is very lovely). Instead I would love to check out the MGallery Hotel Rezydent, which is in an almost equally impressive building, but even closer to the city centre and the train station and not as expensive.
Some pictures of the hotel: