I think the production is solid, not really spectacular but the album sounds pretty good. I never really understood complaints about it being too "commercial." Kurt Cobain's poppier songwriting make the album commercial, not the production, and if you compare it to what else was going on before it came out, it's pretty darn grungy.
I've got a problem with Nevermind : every time I listen to it, my opinion changes. Sometimes it's great, sometimes I feel bored. I just listened to it last week, and I guess I've come to a settlement.
I guess I'd give it a 3.5/5.
"Smells like" is still a great song (5/5)
The other singles are great and I love track 2
The rest is decent to boring to my ears.
About the production, I don't feel a gap between the songwriting and the prod so I guess it's OK
Cobain couldn't stand the commercial success of "Nevermind", so I guess that's why he called the prod "slick".
But to me it's really their best album, just THANKS TO THAT.