Liam Neeson stars as Bryan Mills, the action-hero ex-spy father of the annoyingly bubbly Kim Mills (Maggie Grace). He's a pleasant enough old man, until you kidnap his daughter and piss him off, at which point he will stiltedly tell you that he's going to come and kick your Albanian ass, along with the asses of half the population of Europe.
In terms of plot, there's not much new ground covered. The film draws heavily on its action predecessors—Neeson is "getting too old for this shit," but he "just wants his kid back," and presumably he's also "sick of these motherfucking snakes on this motherfucking plane."
I recommend getting there a half-hour late. You get to see Liam shoot his friend's wife in the arm, electrocute an evil foreigner, and beat the crap out of a cadre of thugs with nothing but his wits and a fire extinguisher. And once the awesome gruff-talking, car-chasing, foreigner-kicking fun is over, get the hell out of the theater before you have to see any ridiculous heartwarming crap.