I think Kreia was an extremely well-written character - she was the driving force behind this game, and the main reason why I enjoyed it so much.
Her complete neutrality made her interesting. I've never seen a character quite like it before. In KOTOR1, the things you did were either clearly dark or cleary light side.
"Look. It's an old woman. She needs money. Will you give her some?"
" - Give the woman 10000000000 credits. Because you can afford that."
" - Do nothing."
" - Kill the woman and take her money. Ahaahaha. You're so evil."
Especially on Nar Shaadaa, Kreia tries to show you that the things you do have more consequences then you realize.
Kreia made KOTOR2 seem much more... real than the original did. She made you realize that the black/white scenerios we were used to in K1 went deeper than we know.
(Sorry for the ramblings, by the way. I just joined, so.. yeah. Might as well ramble on about something I like than complain about something I don't, right?)