Couple of tips on John Pennekamp:
There is an admission fee--I've seen people complain about this, but it's not bad, honestly. It's $4.50 for one person, but the fee goes down with the number of people. We had 7 people in our party and it only cost us $11.50 total to get in.
We had made reservations ahead of time for the glass bottom boat ride (you don't have to pay anything until you show up), but when we went to check in they told us conditions were "moderate to rough". A local told me if the captain says it's "moderate to rough" it means, "Don't go!!" We were disappointed not to do this but given my small children were glad we didn't have to deal with seasick kids for 2 and 1/2 hours as that wouldn't have been fun for anyone.
The park's beach was very crowded. It's not really a place to relax during the busy season (ie. Christmas holidays). We hiked the trails, looked for some geocaches. Disappointed in one trail as it appears to lead to an overlook tower, but all the routes were dead ends as they were doing repairs and you can't get there right now. Wish there would have been a sign to that effect.
My kids really did enjoy the aquariums inside the main center, that had some cool fish and corals. You can definitely spend some good quality time here but I think you need to pick your days carefully to avoid the crazy crowds.
Also, there are poisonwood trees (like poison ivy) on the trails, and any of the parts of these trees will cause bad reactions like poison ivy. They are easy to spot but if you don't bother to read the sign you could get yourself in trouble as they are all over the trail and it would be easy to lean on one or touch one without realizing it.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.