The case against him (pdf) is interesting, because beyond just going after him for helping to distribute illegal drugs, they claim that he solicited a Silk Road user in a murder-for-hire request (though he's not charged with that), to potentially go after a different Silk Road user who was threatening to reveal the identities of people on the site (the user claimed to have hacked a large vendor's account, and demanded $500,000 to not reveal names). They also go after him (of course) with a CFAA violation claim and a money laundering claim. Of course, we've seen the DOJ inflate and pile on charges against people in the past, so it will be worth watching to see what details come out of this -- but soliciting a murder, if true, seems like a fairly big deal.
In addition, the complaint against him claims that Silk Road generated 9.5 million Bitcoins in revenue, leading to 600,000 Bitcoins in commissions (or roughly $1.2 billion in sales and $79.8 million in commissions). Of course, that seems noticeably higher than previous research had suggested. It also notes that the FBI itself made over 100 purchases on Silk Road -- including ecstasy, cocaine, heroin, LSD and others. Apparently, they wanted a lot of evidence. And, in case you were wondering, the FBI informs us that their orders "have typically shown high purity levels of the drug the item was advertised to be on Silk Road."