Nirvana were cool, I used to play all of their songs when I was begining Guitar playing.

I suggest you start learning Led Zeppelin,GNR ,Metallica, Megadeth, Pantera , Aerosmith, Scorpions, Pink Floyd, Deep Purple, Jimi Hendrix, AC/DC , The Beatles ...

You should also consider playing stuff like Satriani,Vai,Jason Becker and Malmsteen.