What makes 90s music sound like 90s music?

Sorry if this is too basic for words, but I'm interested in knowing what is particular about 90s music. Is it a chord thing, a structure thing, just a lot of guitar? Think, Gin Blossoms, Hootie and the Blowfish, even Stone Temple Pilots.

Bonus question? I heard someone say once that rap and country have the same structure. My husband has never heard such malarkey. Thoughts?