It's not just the themes that are disappointing- I can chill out to Biggie rapping about how he shoots people 24/7- but the lyricism and technique in a lot of hiphop/pop is just awful.
I think hip hop became is suffering from too much contamination from other genres like rnb and a bit of pop, i don't the style has changed so much all over the years, but again we are talking about hip hop, but there are still some underground and less known hip hop made that has the vibe and feeling from the early days, the problem is radio stations don't play it anymore.
It is really shocking how bad some rappers' flows are. Hope this works as a temporary pick-me-up. :)