Stats 101, pinside staff take notice:
Median versus Mean
The mean is commonly known as the average = sum / number_of_items
The median is the mid-point of an ordered list of items. If the number of items is even take the average of the 2 middle ones.
Example:
The ratings for Some machine are: 7.8, 8.5, 6.9, 9.2, 9.0, 8.7, 7.0, 8.8, 7.9
average = 73.8 / 9 = 8.2
median = 8.5 (if you order the above list of 9 items 8.5 is the middle)
Now Joe Hater votes the game as 1.5
average = 7.53
median = (7.9 + 8.5) / 2 = 8.2
Instead of Joe Hater we have Joe Enthusiast vote a 10
average = 8.38
median = (8.5 + 8.7) / 2 = 8.6
The median is not nearly as susceptible to enthusiasts and haters as the average and therefore gives a more realistic rating. Outliers have a much higher tendency to affect the average but not the median.
Another example would be income. Bill Gates that makes 1 billion a year plus 1000 homeless that make nothing (= 0). On average they make about 1 million a year each, while the median being at 0 reflects more accurately the true nature of the situation.
If you have many items in your list, like 100+ votes, they tend to be very close together. In this case outliers on either end would hardly move the median when compared to the average. In the income example add Warren Buffet with another 1 billion in income. Now the average moves up to almost 2 million per year while the median is still at 0.
I think the income example best illustrates the flaws of taking the average instead of the median. So if you want to cut out the nonsense, take the median and not the average.

If I played the game I rate the game, it as simple as that. There are some games that are not finished, like CC or more recently Magic Girl. Once I play on an finished or upgraded version like CCC, I can change my rating of the game accordingly to reflect the improvements made. So far DI is a great game in the condition I played it in 11/2016 at Florida Free Play. Maybe it will be better at time of release, then I revisit my rating of the game.

How do I make a purchase decision?
I look at the rankings to see what games other people like. Then I find a show or arcade where I can play several of those well liked games plus whatever else happens to be there. Some I like, some I don't. Some are over- or underrated in my humble (but correct) opinion. I know, personal tastes vary. No biggie. Once I found some games I like I watch the market for nice examples that are reasonably priced.
I love going to pinball arcades, expos or collectors home to play a large variety of games, but in the beginning the ratings helped to give me a direction of what to look for. I would not spend $$ for a flight, hotel and show tickets to play machines that are ranked in the bottom 100.