This one gave me the creepiest vibe of all I visited that week of the vacation, mainly because it A) was down a set of railroad tracks, B) was about to rain, C) had very distorted limestone formations, and D) had many places to fall into the run. Literally, the path down to the shore was slanted at about 30-degrees, and the slope went down into a hole in the limestone, right into the dark run.
It is definitely a site to see; the formations and the way things have generally fallen apart/been built up are spectacularly unique in the Florida springs world. It's scary, it's wild, it's strange, and that's enough to warrant a visit.
I downgraded my opinion of this spring to a "minor" spring mainly due to the difficulty of access (legally) and the danger of the area. I've read on the net that the spring is a popular diving/scuba destination, but the thought of that is almost too much.