I finished the main campaign in Borderlands (DLCs pending yet, but I don't think my answer is there), I reached the Vault, was expecting riches that'd blow my mind, and all I got was one big monster.
Perhaps I missed it in some dialog, but what was the point in opening it for that? Was the plan of the woman that guides you throughout the game for you to kill that monster?
She even says that the vault cannot be opened again for 200 years, will the monster re-spawn then and has to be killed again?
Was the monster protecting something? If it was, why not entering the vault after killing it?
I really liked the game but was disappointed by the ending (or most likely didn't get it).