The goal of terrorism is to cause terror. Was the US sufficiently terrorized by 9/11? It'd be near-impossible to argue that we weren't. Not only did we shed quite a few civil liberties, and subject our own citizens to a wide range of inconveniences and violations, but we also spent trillions of dollars in an ongoing "War on Terror" that seems to have no end and no realistic, tangible goals. (As with the "War on Drugs," it reifies an intangible concept, and then attempts to fight that concept as if it were tangible).
Getting the US out of the Middle East is a long-term goal of Al Qaeda and similar organizations. But the short-term goal, i.e., how they plan to get us out of the Middle East, is by causing our society to collapse -- financially and socially. To paraphrase one of OBL's treatises, Al Qaeda wants to "bleed" us to death. Terror is their chief tactic in pursuit of that strategy.
OBL is dead, and depending on whom you ask, Al Qaeda is either spent or significantly weakened. But that's sort of beside the point. Those guys never really expected that 9/11 would cause us to withdraw immediately from the Middle East. In fact, their entire plan was to draw us deeper in, where we could waste blood and treasure and engender further ill will in the region. And the fact that we whipped up a security frenzy in our own country (PATRIOT act, airport security theater, paranoia, etc.)? That's either icing on the cake, or part of the cake itself, but it's certainly a big win in Al Qaeda's column.
Now, if you take the long view, you could argue that there's still time for us to correct our course. The terror and repurcussions of our reaction to 9/11 can still be undone. We recovered from McCarthyism. We recovered from the Alien & Sedition Acts. Time and again, our country has temporarily threatened its own principles or abandoned rationality, and then come back to its senses in the long run. It's entirely possible that the post-9/11 security frenzy ends up being another historical footnote.