Ask HN: How do you (would you) assess an ecommerce application?

I'm the lowly developer on an ecommerce selection team with a large group of business people who are focused on the eye candy and features. I'm trying to explain that the features and presentation, while important, is paint on the house compared to the overall architecture of the application/solution. There are a lot of important aspects to consider (Security, extensibility, performance...) How would you come up with a definitive list that would define 'What defines a good ecommerce application?'