She is certainly very beautiful. And while she's not noble, she is Spanish and that will make her adjustment to royal life a bit easier. Unlike Mary, she will not have to learn a new language or culture, and that is one less hill to climb!
And because this relationship was kept so secret and hush-hush for such a long time until now, Letizia has not been subjected to the level of scrutiny Mary was prior to her engagement announcement to Frederik. Probably less stressing in some ways but more pressure on the day of the official presentation.
I'm curious to know what she is like personality wise, and how she'll fit in into the women of the royal family, from the properness of Queen Sofia, to the formalness of Infanta Elena, to the casual, sportiness of Infanta Cristina.