Noam Chomsky as a linguist? Incomparable. Like Newton, Einstein, and Hawking to physics, all rolled into one. Even beyond linguistics, the stuff this guy has done has rippled through everything from psychology to computer science. He's a legend.
Noam Chomsky as a political theorist? Bit of a whack-a-doo. Sort of lives out on the socialist/anarchist fringe. Likes to be outrageous, a little bit of a bomb-thrower. Like other people who spend a lot of time in the theoretical world, he tends to oversimplify foreign policy, international political economy, and economics in order to promote his own views "logically," while glossing over or missing entirely facts that don't quite fit his framework. He's kind of found his unifying theory for the world, and it's sort of a labor-oriented anarcho-communist struggle against authority, tradition, and convention. I struggle with Chomsky because there are a lot of things that he says with which I agree, and there are some things he says with which I disagree but can understand and respect his views, but then there are things that he says that are just tinfoil hat, howl-at-the-moon loopy.
All of this is my opinion, of course. I'm sure a lot of people find Chomsky's political beliefs totally reasonable. But when he said that Obama ordering the hit on bin Laden was equivalent to al Qaeda attacking George W. Bush's "compound" (his words, and I believe it's called a "ranch"), killing him, and dumping his body in the sea, he just sounded like a crazy old man to me, desperate to be seen as a "dangerous, radical outsider." He actually compared Bush to the Nazis, and claimed that Bush was responsible for all of the sectarian conflict in the Middle East. Funny that the equivalence wasn't between Obama (who signed off on the hit) and bin Laden, but not terribly shocking considering the source. That's pretty much textbook Chomsky. He tends to view anything that a Western, 1st world power does as sinister, fascist, and immoral, while unconditionally embracing any non-Western, developing nations regardless of the deeds (or misdeeds) of their governments. It's a shame that he doesn't apply the same intellectual rigor to his political views, but, whatever. Any time something can be crammed into the radical revolutionary narrative, he's on board, facts or morality be damned.
As a matter fact, I'd be curious to hear what his thoughts on Syria are.