I don't know what they could make a sequal about. Exploration played quite a part in the game, and considering you seem to have covered the entire world by the end, there wouldn't be much to continue the story. Besides, why mess with perfection?
Anyway, I'd say my favorite scene in this game was at the end of the ice continent. [spoil]The stuff with Drachma was pretty dramatic, but I liked it mainly for the "it was under your nose the whole time" factor with finding out what the purple Gigas is. Also, I went in there prepared to have another Gigas battle.... kind of a relief that it was all just a cut scene, especially after spending about an hour fighting the previous Gigas.[/spoil]