Even if they didn't have the expansion, it still was a pretty interesting ending. Remember, Diablo had the ending where after you delved so far into hell that the horror down there was too much for him to handle and he killed himself.
Though the expansion will make the whole thing interesting. I'm going to play threw it again after the expansion is released and I'm sure that it will make what we already experienced feel like a beta version of the game. It is kind of exciting actually!
