There are two sides to this: One:
Many people go do something incredibly stupid, Get injured or win a Full Darwin award. And then they, or their estate, sues the park (or the building or the ____) where it happened claiming they should have KNOWN some idiot would try to improve the gene pool by his self-removal and they win. or even if they loose it costs the facility thousands in legal fees.
Example, Diving head first into the clearly labeled NO DIVING shallow end of the pool and breaking their dang fool neck. Pool also clearly labeled NO LIFEGUARD ON DUTY.
That said true negligence by the park. Well sometimes that too happens.. In another thread I mentioned mis-wired power pedestals putting 100 amps where zero amps belong and causing an invite to be issued to the fire dept.. I'd sue over that one myself.. But that release, in that case... Well.... The park may have some issues with a good lawyer even with the release.. I mean, THEY SCREWED UP AND CAUSED DAMAGE. The release may not help them ... Or it might, Depending on the court. I can only say how I'd vote if on the jury and odds are, I won't be on that jury.
(0dds are {either six or twelve}/{number of people eligible} to be on a jury in case you wonder and those are very small odds).