This is where the Stones began dipping their grimy toes into various forms of Americana in a big way (discounting, of course, their early career in blues and R&B). The album fluctuates between their laid back form of it, and harder rocking contemporary efforts. And for all of the publicity about how Brian Jones was trying too hard to force the band into new directions, the Stones still sound pretty much tight and together on here.
Interestingly, half the songs on here almost sound like a foreshadowing of their sound on Exile on Main Street 4 years later. One difference is that on BB, they still sounded so ironic when trying out material that's supposed to represent backwoods or down home America; almost like they're slightly embarrassed to be trying it. That would have been unnecessary, as they did a great job anyway. Not in terms of aping or representing some specific standard style from America, but rather in becoming more casual in their ultimate success in creating something uniquely theirs. Note how they lost the irony over the next few years (right after Sticky Fingers, pretty much). And perhaps more importantly, look how loose they would get. Even if drugs did influence that.
All that aside, Beggars Banquet isn't strongly remembered as an album's album. Obviously, the lead-off hit gets played endlessly on classic rock radio, and has made various live and compilation albums ("Street Fighting Man" enjoying a more modest status in this regard). But the album isn't a total stylistic split. "Jig-Saw Puzzle" transcends all their styles up to that point into a slow building something that sounds greater than it really is. And "Salt of the Earth" does a beautiful job of combining their contemporary rock evolution with their American folky approach. It's a great album ender.