It means an explosion, and can also mean fun or great in slang (but it sounds a bit old to me).
Is it true that they use pitsuts in slang for an attractive person? And if yes, both boy and girl or just one of them?
As Wiktionary says, there are two slang uses for פצצה, one is 'attractive' and the other 'great'.
So הוא נראה פצצה simply means he looks great; the same way you can say הבית נראה פצצה. On the other hand, פצצה בלונדינית for example could not refer to a handsome man, only to an attractive blond woman.
Either היה פיצוץ or התרחש פיצוץ. The problem with היה פיצוץ is that it could mean "it was a blast" too.