I signed up to preview the new Google maps and received my invitation this morning. Most of the changes don't bother me, but I noticed Terrain view is gone. I use this quite a bit and I think others do too. If you like it, it might be good to voice your concern.
I noticed one of the staff members replied here:
"The new version of Google Maps is still "new". Please be patient as we make the product even better. In the meantime, there are a few features we don't currently support, including terrain mode."
I'm not sure if this means it's temporarily omitted or completely nixed, but I fear it may be the latter.
Of course there are alternatives. I often use http://www.openstreetmap.org/
-- however, I always went to Google Maps first.