I really wanted to go for 4.5, but no halfsies. Every time we go to Vegas I HAVE to come here and see what the latest display is. It has almost always been amazing (one time it was a bit lame, but I think it was about trees or something that time). When they do people it is really a sight to behold. If you aren't into flowery art then you will be in and out in 5 to 10 mins....unless its really crowded and that time may get upped if its crowded with people standing in the middle of walkways taking pictures like no one else might want to walk that way. If you really like this type of thing - or if you are one who wants to take snaps, but not block the pathways - then you could spend a bit more time there.
The Christmas displays are always the best to me. I would put it on the list of must sees when visiting Vegas.