A Jew becoming Orthodox should never lose his personality. Changes in personality for the better are a good sign. If someone becomes sullen, withdrawn, irascible, be alarmed. He is in some sort of danger, and possibly taking drugs. It's even possible that he has joined a cult.
Many cults depend on secrecy.
They talk about a truth that no one else has. Judaism claims no such secrets. The Torah is open and available to all who wish to learn. This website, and the many Orthodox-Jewish sites on the web prove that. Judaism, in fact, teaches that one does not even need to be Jewish to go to Heaven.