This one one of the more expensive lunches I had in Spain, and one of my least favorite. Everything…read morewas good and fresh, but it was just missing the wow factor. I think you are paying more for the experience of picking out the items. It seems like a bit of a tourist trap. It was early on during my trip, so I didn't know better at that point. It's also partially underground, so the atmosphere is nothing great which is a shaven when you're right by the beach.
Surprisingly, the best dish was the fried calamari. It was so tender inside and crispy outside. It actually had flavor unlike most of the frozen stuff in the states. The octopus was my least favorite. It wasn't as tender as it was at other places and had less flavor. Langostines were good, but not as good as ones I had elsewhere. Clams had some shell/grit in them, but the flavor was good. The staff were friendly and helpful when I was trying to decide how much to order.
If I return to Sitges, I would try a local restaurant for lunch instead. This place is a chain around the Barcelona area so you can have many opportunities to try it.