It is a hugely major attraction, definitely the biggest deal since they built the Tower of Terror!
Only a few people (imagineers, execs, focus groups, etc) have ridden it so far, but initial reviews tend to be very positive. Cast members will be able to ride it starting this week, followed by guests within the next few months (definitely by August 15, when the official guest previews will begin).
I have a FAQ with tons of information about this attraction on my web site if you are interested in further information about it.