I've never played Descent, but I'm really looking forward to this coming out.
From the announcement:
Fantasy Flight Games is proud to announce seven new Ally Packs and Villain Packs for Imperial Assault! You’ll be able to highlight iconic characters from the Star Wars universe in your games of Imperial Assault with these figure packs:
-Han Solo Ally Pack
-Chewbacca Ally Pack
-Rebel Troopers Ally Pack
-Rebel Saboteurs Ally Pack
-General Weiss Villain Pack
-Royal Guard Champion Villain Pack
-IG-88 Villain Pack
Like the Luke Skywalker Ally Pack and the Darth Vader Villain Pack included in the Imperial Assault Core Set, these new figure packs contain detailed plastic figures to replace the tokens provided in the Core Set. These figures can be used in both the Imperial Assault campaign game and the skirmish game, and every Ally Pack and Villain Pack offers you new missions for both games.