What makes a record collection "great"?

A 'great' collection isn't the same as a 'large' collection-for a collection to be 'great', it must be completest within it's own specific genre, including a historical perspective, and a large number of rare or unusual recordings. Let's look at, say, jazz. A great jazz collection would, by necessity, be a very large collection-tens of thousands, at least. However, a more specific 'Coltrane' collection, or 'Blue Note' collection, could still be great within it's specific subcategory, but require a library of far fewer recordings. Put another way, this guy http://superbizzee.blogspot.com/2009/05/ballad-of-record-rama.html who's been trying to sell his collection for years, supposedly has 3 million records, including 1 million lps. Without knowing the specific titles, all I can think of is that, in the long history of the lp, they put out millions of really, really crappy records.

just my opinion, of course. And for the record, I have a relatively 'large' collection, but nothing really 'great'-even though I 'greatly' enjoy it.

It's not the size that matters- it's how you use it.

It has your favorite albums

two things
first, if you think it is a great collection it is
second if it has what you want in it

Just like a library. A library will have within it "collections" that would be prized.
I have a large collection that is comprised of different genres. Depending on your tastes you may find that parts of my collection are "great". Some may find that jazz alongside country or psychedelia would make for a wierd, not great, collection. Collections within a collection, like a library.
Anyway, who cares if it's great if it pleases you, whetherit's 10LPs or 10,000LPs?!
;^)