The book began as the story of supervillains masquerading as superheroes, and eventually coming to rather enjoy the change. It then morphed into a fighting area type book. Then a government sanctioned black ops book. It's now kept much of that, with a mutual assistance side to it, missions taken to help out individual members as well as matters of national security.
Well, I'm told after Original Sin, to expect the nature of the book to change dramatically.
To what, I've no idea. Maybe the tales of the Thunderbolts crochet circle?
When reached, Marvel declined to comment.