La Mar is a really brilliant place in many ways, though not cheap. I'm actually partial to Punto Azul for ceviches, as they're also a very popular place, but with lower prices and bigger portion sizes and always fresh-tasting. La Mar has more varieties, though, plus a sampler option. With both places it's good to get there early (at opening or shortly after) as the crowds build and there's a wait otherwise, especially on weekends.