Sam has changed. If in Double Agent, he's had to balance trust between Third Echelon and the bad guys, in Splinter Cell: Conviction, Third Echelon's trust in Sam Fisher (and vice-versa) goes out the window.

Sam has changed. In a special coverage of behind-the-scenes, Ubisoft Montreal Narrative Designer Mary de Marle revealed to IGN the changes to Sam's profile and gameplay. Sam returns to find Third Echelon a bureaucratic mess and hiding a shady conspiracy, and a threat to a good friend and comrade from back in the Splinter Cell day, and so he must now face off against his former employers.

Sam has changed. Out of Third Echelon, he no longer has access to the NSA's grab bag, and thus a lot of gameplay will change from that we're familiar with in previous Splinters:

• Sam's down with the hood. As you can see from the IGN screenie, gone is the iconic black suit, replaced by a more comfortable set of hoodies and jeans to hang with one's homies. This is deliberate: instead of hiding in the shadows, IGN reveals that Sam will have to blend with the crowd, Assassin's Creed-style. And the hoodie helps: pulling the hood over the head decreases recognizability from the authorities.
• Aside: why do we expect - with great trepidation - a ton of "Assassin's Clones" remarks in the comments?
  

• Sorry, only carry-ons allowed on this flight. That shoulder bag Sam's carrying also represents the limited amount of gear he can take with him at any one time. Instead, Sam will have to rely a lot more on his environment as a tool and as a weapon. Less high-tech and more street-smarts.