They're adding trophy/achievement support, new content, and doing the entire game in HD. The cut scenes will probably be absolutely outstanding, where as the gameplay will get an HD remix (like all the other HD collections coming out)
That, and it's possible they'll redo XII and X-2 with it in HD also, I think yeah very worth it. X-2 storyline was was absolutely terrible, the gameplay wasn't that bad though.
“There are three things all wise men fear: the sea in storm, a night with no moon, and the anger of a gentle man.”