Nirvana is for me, one of those bands I have a love-hate relationship with. They were very, very popular and around when I was younger. They came around at just about the time I was old enough to figure out that giving authority the finger was fun (if kind of immature). I still liked them through my high school years. In fact, whenever I listen to them today, it's usually only for nostalgia purposes. I don't think they're particularly good, or able players...okay, Krist and Dave sort of got off the hook, but by my standards, they're both fairly average.
What I'll never understand are the kids getting into it today. It was a band largely defined by the time they came to fame. The 1990s were a huge reaction against hair, speed, and thrash metal and 80s balladry/soft rock/new wave...hence bands like Nirvana, Silverchair, STP, etc. Actually, Nirvana is just about the only grunge band I can stand. I pretty much despise every other band to add its two cents to the 'movement' of staring real hard at the ground and playing braindead chord progressions. There are plenty of mainstream rock-radio bands around today that I think are better songwriters and musicians than Nirvana.
To me, they're far, far from the best band ever to come around. Not by a long shot. I don't mean to poke anyone in the ass by saying that, but it's what I think, and I actually like them.