The 15-85 range is shorter. I suggested it since you mention landscapes and fact that it matches quite closely to the range that you would be used to on the G11. Besides, 15-85mm is noted for it's picture quality, probably second only to the 17-55mm for EF-S lens. You can read reviews for that. Well, if you get lousy pictures you can't blame your gear, right?
You need to convert all to 35mm equivalent for a more meaningful comparison... so again:
G11: 28-140mm
18-135 kit: 29-224mm (greater reach or more "zoom" in layman terms)
15-85 lens: 24-136mm (do note that the 4mm diff at the wide end is more significant that the long end compared to the G11)
It's your call.
thanks!