As I understand it, this is a slang word in this context, and is used in this way when the speaker is impressed positively or negatively by something
"That's some rain!" - about a heavy rain
"That's some good stuff!" - about something very good
"This is some vacation"/"Some vacation this is" - when a vacation is going extremely good or extremely bad.
"Isn't she something?" - about an unusually smart, resourceful or otherwise impressive girl
It is also used sarcastically, meaning the opposite.
"Some gentleman he is" - when describing a person who claims to be a gentleman, but does something rude.
I'm not a native speaker, but I hope this helps!