You get NG+ after reaching the end of the game... but since the game isn't done the only available ending is to let order drop to 0 and fail.
Then you can restart at whatever difficulty you choose, and keep your titles for some fairly major stat boosts but go back to level one allowing you to try different builds and playstyles (and collect a different set of titles to pass on to the next playthrough, if desired).
If the last time you played early content was before the big v0.6 update, I definitely recommend starting over if you have time because the whole desire system was reworked to produce a better corruption narrative, but if your previous playthrough was only like a month ago there probably isn't much new content, and what there is can probably be experienced just as well at high levels.
