Just how bad/good is the 18mm?

Eagerly waiting for the XE1, with the kit zoom. I was thinking of selling my X100 and buying the 18mm so I can use the XE1/18mm combo in it's place. Reading this forum, I see mediocre reports on the 18mm and the X100 is so good... how bad/good is the 18mm? Will I lose a lot of sharpness and/or IQ compared to the X100?

I know the 23mm is coming, but it's not here yet, nor do we know how good it is....
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= John
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