Both games contain improved maps and character models and textures as well as improved lighting, shadowing and enhanced pre-rendered movies with better quality in high definition. Trophies for both games will be added. All controllable and other major characters have new character models, and monsters and minor characters have rearranged textures to improve quality. The game now plays at 16:9 widescreen and some scenes have been adjusted with different camera angles to accommodate for it.
The idea for the remastering came about when Square Enix met with some of the voice actors during the making of Final Fantasy Type-0 and realized they hadn't met since the making of Final Fantasy X, and how it would be fun to do something for the game's 10th anniversary. However, they missed the 10th anniversary of Final Fantasy X in 2011, but lucked out with 2013 being the 10th anniversary of Final Fantasy X-2.
SOURCE: Came across these photos on the FF Wiki
I hope we get teased with some X-2 caps soon! I'm excited to see how they cleaned this mess: