The production for one thing, it lacks the glossy sound of Nevermind, it's much more lo-fi... Less bass, more guitar, more fuzz and feedback, and a much more agressive and noise oriented sound than Nevermind... The lyrics are better as well.
Cobain thought Nevermind came out too well produced, and that he wanted to revive a more primitive sound similar to what he achieved with Bleach.
And i would say that most of the album isn't listener friendly, at least not most of the tracks aside from the singles.
Also indie banRAB can get radio play too, Float On is a big mainstream radio hit.