I have completed the game and wish start over again. However, after creating a party, I found out that the game is not a "new" game. The map has already been mapped out, the emeny that should been there no longer exist. The question is how to start an entire new game? After killing lord Cet, does it consider me completing the game or did I miss something at the end?

All you have to do is go into setup, next to load/save and select "Reset Adventures" That will restart the game and the next time you come out of the inn in Valeia, you will meet Gareth.

Thanks.

Alternatively, you can delete all yor saved games, (but not the folder).