This British princess is just about as perfect as they come: she's wise, beautiful, resourceful, and—most importantly—she's honest. She stands up for herself to her dad and notices the Queen is a "dissembling courtesy" (read: faker) right away (1.1.98). While she mourns the banishment of her husband and moans about having a "foolish suitor" (Cloten), she doesn't wallow in self-pity (1.6.2).
Just about everyone recognizes Imogen's beauty. Of course her husband thinks she's hot, but even cynical Iachimo calls her a rare "Arabian bird" (1.6.20) and "most rich" (1.6.18). Cloten wants her, Iachimo steals her, and Posthumus wants to die without her. She's one catch all right.
But she's not just a pretty face. Beneath her beautiful exterior is an honest and intelligent woman. She's also faithful: she keeps her vows to her hubby even while he's off betting on her, and even after Iachimo tells her that Posthumus is getting a little too friendly with the local ladies.
Unlike her husband, Imogen trusts in her marriage vows and won't break them. It's her desire to help her husband (by hiding the chest of jewels) that even presents Iachimo with an opportunity to steal her bracelet.
In this play, nice girls finish last... until the very end, when they come out on top.
As if that weren't enough, Imogen charms herself into the hearts of her brothers and Belarius as the boy Fidele. After just a short time with her, Arviragus says, "I'll love him as my brother" (3.6.83). He and Guiderius are enticed by her "angel-like" voice and her charisma (4.2.62), and it's not long before they claim to love her more than their own father—or kidnapper, if you want to get technical.
Imogen's stint in a man's clothes shows she's not afraid to take advice and get the job done herself. When Pisanio presents her with male attire and a plan, she doesn't look back. Like Shakespeare's other cross-dressing heroines (Viola in Twelfth Night, Portia in The Merchant of Venice, and Rosalind in As You Like It), she goes after what she wants. She doesn't wait around for someone to convince Posthumus that she is innocent; she hops a boat to Rome to get the job done herself.
It's only right that Imogen gets a happy ending: after she's suffered through the whole play, we're rooting for her to succeed. She's the one who notices the ring on Iachimo's finger that solves the puzzle in the end. She doesn't accuse first and ask questions later, as others in the play do (we're looking at you, Posthumus).
Even when her name is slandered, she stays calm and collected; and when Iachimo opens his nasty trap, it's Imogen who says to Posthumus, "Peace, my lord, hear, hear" (5.5.265-266). Imogen is pretty much the only one calm and smart enough to get everybody on the same page. It's her actions, actually, that stop the war between Rome and Britain.
We'll sum it up for you: Imogen is the whole package. She's got brains, beauty, and morals—and she's a cool cucumber in some truly sticky situations.