I ate in the 'underwater' one about 2 years, but was in a private room, not in the main restaurant.

The 'submarine' to the restaurant is a bit of fun, if a bit tacky (this seems to be a theme running through the hotel). We had a 5 course tasting menu that was mainly made up of seafood (again I don't think this was main restaurant menu, but one chosen for our group by the organiser). The food & wine was good, but not memorable. It's an interesting place to visit & like no other restaurant I've been in, but the food is very average.

I did not see any prices but I understand you are looking at about £100 per person for the food alone. Wine will also be suitably expensive I'm sure.

In conclusion, if money is no issue then it's a but of fun, but at this price I'd be looking for a place with much better food.