So basically, a more explicit look at violence and illegal rackets, not so much the family life of Johnny Boy Soprano. But even then, even with that family life present, we already know Livia gave him a hard time, I'm sure they had their moments of affection, too.

What makes that narrative thread so great is the fact that we always see it from a distance; even the flashback scenes are filtered through the eyes of Tony. They're fascinating, they're great, they're even deep, so long as they're related to Tony - Tony's anxieties, panic attacks, disturbed view of his sister, his uncle, his father, especially his mother (he's seeing Melfi in the first place because of his mother, and so without Livia's character the show never begins).

Take Tony out of the question, which you'd be doing in a prequel, and what you've got is an exercise in pointlessness, a mere cash-in, something, I'd even go so far as to say, completely unrelated to the original series... which might in a way be a good thing, but let's face it, if the characters weren't called Sopranos, we'd be calling it a phony rip-off. It's like a poor, scraped-up second serving for those in the diner still hungry - but this second serving tastes half as nice, because this time they left out the meat. All you're getting is vegetables and few roast potatoes here and there.