Areas include all creatures contained therein unless the spell says otherwise.
Regardless of the shape of the area, you select the point where the spell originates, but otherwise you don’t control which creatures or objects the spell affects.
That’s the rule; you have no control over the spell by default, and that includes protecting yourself.
“Centered on you” is not an exception
Nowhere does a rule state that things that are centered on you have any exceptional rules about which creatures they target; that is purely a matter of what options are available to you for centering the burst.
You are your own ally... probably
You count as your own ally unless otherwise stated or if doing so would make no sense or be impossible. Thus, “your allies” almost always means the same as “you and your allies.”
That line about “would make no sense” is problematic in the sense that what “makes sense” is undefined. I choose to interpret as minimally as possible: only in cases where to read “ally” including you would lead to undefined behavior, not merely behavior we think is odd.
Thus, blaze of glory does affect you
When cast as a standard action, blaze of glory sets your HP to −1 after the spell is cast, so any healing it does barely matters (it would only matter if someone readied an action to do something in the middle of the spell, which is only a dubiously-legal choice in the first place). But when cast as an immediate action, it does heal you along with your allies, and since the immediate-action version does not reset your HP, you keep that health.