Via Napoli is one of our favorites as well, but I do know that it gets a lot of not-so-great reviews.
As a PP has mentioned, we have only ever gotten individual sized pizzas...so maybe there's something to the theory that the large sized ones are floppier? I've never personally eaten the spaghetti or the lasagne there, so I don't have any idea as to whether those dishes are always bad or if it was an off night when you were there.
On our last visit in September, we were there on the "Eat to the Beat" package, so in addition to an individual pizza we got the spicy pasta dish a PP mentioned, and I totally agree -- it was incredibly delicious! We also had a very good buffalo mozzarella appetizer and an absolutely heavenly dessert with an Italian name that translates in English to something like "ugly but good"...it was divine!
Restaurants are so tough...we all have such different palates and food preferences, and when you add in that restaurants can also have off-days, it makes it so hard to find one that can be "universally recommended." I'm really sorry you were so disappointed in your meal, OP...Disney food is so expensive, so it stinks when it isn't palatable. I know we have been to a few highly recommended WDW restaurants where we didn't end up liking the food too, so I can definitely commiserate with what you're feeling.