TLDR: Triangle sloped ships are one of a few superior ship designs because they allow one to maximize turrets brought to bear in frontal assaults
One alternative would be a cone. That would have similar advantages, and would actually use less material. Though it would also have some odd effects with the shape of decks internally.
The most significant disadvantage, compared to the Republic classes with their hammerhead bow, is the significantly greater cross-section that the Imperial ships display in most profiles. How being able to bring more firepower to bear balances against being a larger target is difficult to judge. I wouldn't assume that the first is always an advantage, though.