I remember, right around the year 2000 or so, the entire music industry went to crap. About that time, the industry—revenge for Napster, perhaps—began to force a lot of angry and/or trashy rappers onto the world. There's been a few songs that I've enjoyed here and there (I do like Outkast, and they were pretty popular in the early 2000s). And it wasn't just pop and hip-hop: country started going overboard with the formulaic music in the mid-2000s, and in Christian music, Chris Tomlin pretty much wrecked that genre singlehandedly.
A few caveats, though:
1. There's still good music being made. It's just that with so much of it being made, and with so little talent in terms of A&R, a lot of it is getting buried and harder to find.
2. There have been a lot of crappy songs in the past, too. The 1980s, for example: when they said "video killed the radio star," they were not kidding! Synthpop makes me gag, and it annoys me that it's overtaking what used to be the "oldies" stations.
3. If you think about it, though, so much of the 20th century was a golden age for songwriting and performing that is going to be difficult to beat. The 40s and early 50s gave us big band ballads, the rise of the blues, and Western swing, the first truly mainstream country sound. The mid-50s gave us rock and roll and some good harmony music with doo-wop (the late 50s was kind of a doldrum), the 60s gave us great sunshine pop, polished soul music into an art form, and fleshed out rock into something new and glorious, and the 70s gave us some of the best songwriting seen before or since.