After visiting a water park, I write a review of it if it is my first time at said park. But if it is a repeat visit, then I write a trip-report I will instead make a generalized review of anything new or already ridden.
In those trip-reports and reviews, I do a rating for each slide ridden and for the water park as a whole. Below is listed how I rate the parks and slides.
10/10 = Amazing
09/10 = Very Exciting
08/10 = Very Fun
07/10 = Enjoyable
06/10 = Decent
05/10 = Rideable
04/10 = Recommend Avoiding
03/10 = Unenjoyable
02/10 = Bad
01/10 = Un-rideable
N/A = Not Available
Luckily, I haven't been on a slide that has hit 1/10! I wouldn't even go on something like that!
So this is what I use every time I rate parks. Slides I can recommend riding at least once will be anywhere above a 7/10 rating.
Anywhere between 5/10 and 6/10 is your choice. If you skip it, you're not missing much.
Anywhere below 5/10, I wouldn't recommend riding.