I hadn't been aware that GKMC was being considered "classic". Except for Kanye's MBDTF, the last few years I haven't thought about any album in that context, my favorite albums just end up on my end of the year list. As GKMC probably will, probably in the #1 spot.
But I wouldn't say it's a classic, and pretty much whatever else I believe has already been stated very well by that Star Slight and Argentine post. Though I will back the side that says TCD, LR and MBDTF are classics.
About GKMC, you might be interested in reading this
. Very relevant to this volatile topic.
It's an interesting review war/debate that I dipped into myself a couple of weeks ago under the username laralogic.