5-stars is perfect. No flaws. The work, the crowd, the atmosphere, the stakes, etc. It doesn't get thrown around lightly. Many have what's called "the five star fear" and never give one out. I went like 10 years without doling out a 5-star. It's like saying something is so good, that you can argue it's the best of all time and meet practically zero resistance.
It's a harder curve, than say, a 5-star movie or album or book. It's intended to be rare. Can't be tossing out the 5-stars all willy nilly. You can lose your nerd cred that way. If you slap the 5 on something, people are going to watch, and you better be right.
Hope that makes sense.
EDIT: **** is considered "great". Anything over 4-stars is generally in the running for Match of the Year most years. ****1/2 or higher is a serious MOTY contender practically any year.