I have not seen the Elvis show, but a trusted friend and his wife are both huge Elvis fans and have seen every Cirque show on The Strip. They saw it early in the run and said:
"Nice show, with some great moments but had some really bad moments as well."
Still, they both want to see it again - after the producers and cast work out the kinks.

Don't know if that helps, but again - this is a couple who have seen about every show here in Las Vegas and I consider their reviews to date pretty on target - so take if for what it is; one couple's opinion.