You can still visit individual inboxes even though the all inboxes option is there.
All Inboxes is my life saver, btw. I have 7 or 8 email accounts at any given time, and can't remember for the life of me which email I used to sign up for something, or in what inbox a certain email is. Being able to search across all of those at once and see all of them in one list has radically sped up my email handling. I hardly ever turn on mail on my Mac now, I don't need to use a computer or go to the web for most of my email things.