One of the best hip hop albums of the decade and it barely moved any units, it's a damn shame.

Others:

Freeway - Free At Last (people talk about Free's debut all the time but this album is just as good, if not better)
De La Soul - The Grind Date
Wu-Tang Chamber Music

Regarding SC & ToT, SC is a classic and went gold, and ToT is a great album loved by most hip hop heads. In terms of sales, sure they were 'slept on', if you're judging by whether or not they went plat, but as far as the quality of music goes, they're far from it.