We had all good experiences. I'd recommend you thoroughly check the duties required and if they're agreeable to you then go for it. It's not like it's going to be an ongoing 'job'. You can certainly last for a one-time thing. Just don't take it and quit mid-season. That really puts a bind on the park and on the other volunteers who have to cover for you.
We've gotten the majority of ours by actually being in the park at the time of applying or know of the park so there were no surprises on either end. Sometimes it's an advantage for the park employee to meet you in person. Some parks might sound nice but the immediate area may be too remote for you - not enough to do on your off time.
We've done national parks, state parks and fish hatcheries. National parks won't require you to clean the bathrooms. They have paid employees to do it. We also found that true of some state parks. Ask if that's not something you want to do.... and yes, it can definitely be eye-opening. Some people are absolute slobs.
Some parks also have interpretative positions which are fun - like working with children or leading hikes. We gave lighthouse tours in Oregon and Michigan. Some would have you working in the office or the entry booth. Ourselves, we wouldn't want one that all you did was sit at the campsite. We like to 'do' things.
You won't or shouldn't be responsible for any kind of enforcement of rules. That should be the rangers job. Ask.
Volunteering is very rewarding if you do it for the right reasons - helping out our parks which is much needed. If you're only doing it for a free campsite you'll find a lot to complain about and you won't enjoy it.