They were the biggest commercial success of the Seattle grunge scene (due to label push), but in the same time one of the weakest if not THE weakest offering of said scene. "Bleach" is a good example of just how weak, lost and in deep need of other band influence to find its groove Nirvana was compared to the rest of the Subpop catalogue of 1989/90.
There are few things about Nirvana that most of people probably missed:
One. The Nirvana sound, as you know it, is not really Nirvana sound. When Nirvana recorded "Nevermind", they couldn't agree on a mix with producers and label and after numerous engineers they brought in Andy Wallace (the dude behind Reign in Blood by Slayer) who did final mix. Cobain stated many times in release interviews that the band was unhappy with the sound Wallace created, few years later Cobain even stated he was embarrassed about what "Nevermind" sounded like. The sound and tone that brought fame to Nirvana was a result of agreement between producer Butch Vig and the mixer.
Cobain was also unhappy with the sound and mixes of "In Utero" and lack of agreement between him and label nearly shelved the album.
Nirvanas shot at stardom, between Paul King playing "Smells Like Teen Spirit" video on his "120 Minutes" show for the first time and stop of 94 tour in Rome, lasted two and a half years almost to the day. Most of which Cobain spent retrospectively screwing his bandmates out of money (lookup album royalties true story). After his death, his wife tried to screw them out of remaining and unpublished releases money (lookup Courtney Love vs Nirvana LLC true story). In 2006 she sold her share of the catalogue to EMI.
Cobain was a copycat. Examples everywhere. "Smells like" riff was ripped off Boston and mixed with
Blue Oyster Cult, the rest was
still Blue Oyster but different song. Nirvana
even joked about it. "Come as you are" was grabbed from
Killing Joke. To name but few. Cobain publicly claimed they were trying to sound like Pixies.
The dollar chasing kid on the cover of "Nevermind", Spencer Elden was on Never Mind The Buzzcocks last month.