You've neglected to give the minimal context, which is:
North American informal
used as a euphemism for ‘shit’:
shoot, it was a great day to be alive
This just an example of the Oxford Dictionaries being out of touch. "Shoot" is not used as a euphemism for "shit" in a positive exclamation, to intensify excitement or awe.
Someone saying "shoot, was it a great day to be alive" would draw smirks due to the quaint awkwardness of the expression.
This substitution is only done for "shit" that is used as a curse, expressing irritation. A much better example is:
Shoot, I forgot my wallet at work!
Common substitutes for "shit" in a sentence like "shit, it was a great day to be alive" would be along the lines of:
Man, was it a great day to be alive!
Damn, was it a great day to be alive! [Note that the "darn" euphemism for "damn" is poorly suited, similarly to "shoot".]
Boy, was it a great day to be alive!
Most words used as curses expressing irritation are not used to intensify awe or excitement. For example "crap" (even though it's a synonym of shit), "darn", "shoot", "rats". These words only express annoyance.
What exactly "it is a great day to be alive" means could depend on the context. By itself, it is an expression of euphoria: it might be spoken by someone feeling elated and optimistic, who has a sense of living to the fullest.