Subject matter is totally subjective.
Kanye is one of those rare artists that we see evolve right before our eyes. Every album, every song, is a reflection of his life and where he currently is at the moment. He is the most HONEST, VULNERABLE artist in pop music today. That has never changed. He as a person changed, but his authenticity has not.
90% of the population will always refer to College Dropout as being the best, subject matter wise. Why? Because 90% of the population can relate to working at The Gap, or retail in general (Spaceship,) and religion (Jesus Walks) and materialism (All Falls Down.) But from Kanye's perspective, those were the major things going on in his life at the time, and he was in that population of the 90%.
Fast forward to Yeezus, people aren't going to be able to relate to it. Kanye is in a different world now. But one thing that remained constant, from College Dropout, to Yeezus, is the authenticity.
As a fan, I have to accept that. I can't go into each album hoping for another College Dropout. It's just not going to happen. And if it did, it would be Kanye forcing it and fake. Kind of like Cam and the Dipset reunion, I LOVED Cam and Dipset but I DON'T love the current reunion movement. So his next body of work, only thing I'm hoping for is for Kanye to continue to be authentic and vulnerable, it may not be a crowd pleaser, but I think we have to respect it for its honesty.