I've played them both. Shadow is a different experience all together...starting with the feeling you get passing through the gates, being greeted by the starter and led in to the clubhouse. The driving range continues the feel the privacy and you take that feeling right out on to the golf course.
At the Wynn, you check in at the golf shop, located at the end of one of the lobbies, next to the club restaurant overlooking the 18th green. Anybody can walk in and out on to the balcony of the restaurant to watch you play the 18th. The couple of times I've spent time in the clubhouse/restaurant at Shadow after the round my foursome is one of two groups at most. There is no comparison.
As far as the golf goes, I think I said this on another thread, Steve Wynn built the course knowing he was going to bulldoze it in a couple of years and build more rooms and residential housing. It's good, but on the "light" side, it just doesn't give you the sense of depth you get on other courses in the league the Wynn wants to play in.
That being said, I enjoyed the golf course, but mostly because it was right out the back door of the hotel, and within 10 minutes of finishing my round I was back at the blackjack table. It's a tremendous value add to the hotel.
Given the choice, for my money...Cascata, Southshore, Shadow, Southern Highlands, Wynn....in that order. And BTW, hopefully it is the casino's money by the time I have to pay for any of it.