(source is Shaman King)
Forgive me in advance for any blunders, I'm very new to Japanese.
I've been under the impression that おお is meant to be romanized as either "oo" or "ou", with a certain preference for the former. While this isn't my first time seeing "oh" (and sure enough, the wiki itself opts to use it, although with a hyphen), I'm pretty sure that this choice mistakenly snowballed into the addition of an exclamation mark, as if the "oh" in question was an exclamation in and of itself, rather than (part of) a name.
As someone with an interest in localization and captioning, I think I might be onto something here. Can any of you back me up?
by arkaser