As the circa-WWII reluctant king of Great Britain, bogged down since childhood with a stammer, Colin Firth is even better than what you may have heard. No one does uptight like Mr. Firth, but, in his posture, and as much in what he doesn't say as what he does, he gives real depth to a character that could have been a joke, or an empty sketch.
(I know what you're thinking: His inevitable Oscar nomination pales in comparison to his honoring as April 2010's Man of the Month, but it's still important to acknowledge these more mundane accolades.)
As for the rest of the movie: It's essentially a bromantic comedy disguised as a period piece. The tension is all based around whether or not stubborn royalty can learn to accept help from a commoner. They bicker, they make up. Secrets are revealed, they have to decide whether or not they'll stand by one another. It's all very touching, in an incredibly familiar kind of way. The sets are gorgeous; Geoffrey Rush is a very convincing Australian; Helena Bonham Carter doesn't do much, but she does have normal skin and hair, so the Academy will probably want to acknowledge this role as a real stretch for her.
7 Twix bars!