I've only been twice. Saturday lunchtimes.
Now you must bear in mind that my favourite meal of the week is lunch ona Saturday, and my favourite lunch on a Saturday is either lobster or Dover Sole meuniere, with a good bottle of poo. On both my visits Rocksalt served these items extremely well, the service was excellent and the view exceptional, so I only have good things to say.
I have no idea whether they also serve the sort of ground-breaking Shoreditchwánk hipsterstuff that you may prefer.
On one occasion I ate next to Victor Lewis-Smith and his mad hair.