It may seem long, because it is rather difficult. But the storyline unfolds very quickly, and there is not so much side quests. All the things shorten the length of tob.
But BioWare was not going to make a new SoA, so I think its quite normal that ToB is so short.
If there were yet an another sequel, that would be great. Imagine that the power of your char in the final battle is only a beginning, a floor to start advancing from... I fear the might of my own sorcerer
