There are many very objective metrics we can use, but even by many creative metrics - it's worse.
Lyrically: have you ever listened to what 2Pac or Biggie were saying? They were rhyming. There was an obvious lyrical flow. Now compare to Lil' Wayne who literally spouts gibberish. Lil wayne 'says words' to 'a beat' and that's it.
Some people point out that 'there's always been bad music' i.e. if you go back to the top 40 in 1977 or whatever it's litered with derivative crap - but - there were many 'stand outs' of great music - even great pop music. For example, Michael Jackson was not exactly an exalted artist in the purest sense, but he was a genius pop artists. I fully respect Beyonce as a hard working and creative entertainer of our times, but I think in 10 years from now, you'll more likely hear a Michael Jackson song than a Beyonce song.
Underlying issues are partly commercialization, but also - 'visualization'. Remember 'video killed the radio star?' - well YouTube is the new MTV and 'how it looks' is as important than 'how it sounds'. Pop stars now generally are more attractive.
Also - it's just too easy to press a button and make noise - people confuse the creativity behind that with raw expression. I saw a band recently that had 2 guys playing 'a computer' and it was interesting, but ultimately very empty. The lack of character has me aching for good, live Jazz. :)
I love Kanye, but it's really hard to get fully behind someone standing there with a microphone, it's like a big Kareoke show.