It's been a really good holiday.
Here, the use of the present perfect reveals that the speaker imagines that the time frame leads up to the present moment. In teacher parlance, there is 'present relevance'. It doesn't matter whether it's the last day of the holiday, or two days after, or one day before returning, or halfway through. All that matters is that
if the speaker sees the time frame as leading up to the present moment, he'll use present perfect, and
if he sees the holiday as a past event, he'll use a past tense. It's that simple. Aspect is about how speakers understand time conceptually. Making a distinction between physical time (as measured by physicists) and psychological time, is very useful here. Our idea of when 'now' is, when the present moment is, is a purely psychological one and
not a physical one.
It was a really good holiday.
This shows that the speaker is thinking of the holiday as a past event or experience. (The meaning of the word 'holiday' is an interesting point to follow, I think, but that's not related to the choice of aspect in this case.)
An old English friend of mine: I haven't seen you for ages! Where
have you
been?
- B: (I've gone to Minsk for only a couple of days and then I'm going back to Moscow) I've been living in Moscow.
- B: (I moved back to Minsk two weeks ago) I lived in Moscow.
The question is about your location during a time frame that stretches from the moment you last saw him to the present moment. So since that's the question, it would be most natural to respond with the same aspect, so
I've been in Moscow is a good answer, and so is
I've been living in Moscow. However,
I lived in Moscow is very odd as it doesn't really address the question (aspect matching). We don't always 'have to' match aspect but it's natural that when someone asks us about a certain time frame, we're going to answer about that time frame directly.
Another very complicating factor I'd point out here relates to the meaning of the verb 'live', which I think is very tricky to understand. The verb 'live' can be understood as both
stative and active. In this context, even though the question is about your
location (it's
not about what you've been doing), you may still answer with
I've been living in Moscow. Although this answer may seem to be about what you've been doing (action), it's actually about your
location (state), so it's a felicitous answer.
- A neighbor I haven't seen in two weeks: Where have you been? I haven't seen you around here in the last couple of weeks!
- (I'm at home = I came back from my holiday some time ago) B: I was on holiday. It was a really good holiday/one.
You see? I don't catch such a thing as matching the tense/aspect, I only use them in the meaning I know they express.
For the reasons I've mentioned above, if the question is
Where have you been?, the most direct answer (aspect matching) is to say
where you've been, which is to say
I've been on holiday. In this case, the entire time frame is only two weeks, so it's very understandable that the speaker still sees a present relevance. If you returned from holiday months ago, that's unlikely. The further back in time you go, the less chance there is that a speaker sees there being a present relevance (this is why many teachers and reference books invoke a 'recent' past) . Again, it's about psychological time, not physical time.