Abrupt actually has many meanings, including coming to a sudden end, and changing subjects very quickly. Both of which the end of the game did.
I think most people would have like to see a scene where order was restored...or perhaps Ashe's coronation...but maybe that'll be in RW.
Anyways, the ending had its good points and bad points...but definitely the final dungeon/boss fights were weak. Which was dissapointing.