We ate at a second Peruvian restaurant in San Jose on our last night there. It was far worse quality-wise than Machu Picchu. It was more expensive (it cost $40 US!) and the food just wasn't as good.
I had a large vegetable soup that was way too salty and a fresh limeade. The limeade was really delicious, but so were all the fresh juices we had had in Costa Rica to that point. Gonzalo had some fish and it was ok. When we asked how they made their ceviche, they said they made it with vinegar (not fresh lime juice). EW! Obviously we did not order it.
If you're looking for Peruvian food in San Jose, Machu Picchu, despite the super-dorky name, is your best bet. Read my review of it here.