Although there are quite a few praiseworthy individual elements of the Little Mermaid attraction, the reason I rank it a notch below dark rides like Pooh, Pan, or even DL's Mr. Toad or Alice (none of which have effects as technically sophisticated as TLM) is the fact that, unlike those other FL rides, TLM is pretty much a straightforward re-telling of the movie on which it's based.
For that reason, it comes off a bit like a Reader's Digest condensed version of a richer and fuller story, and thus a bit flat and cold. The other FL rides generally eschew direct adaptation of a narrative in favor of engendering the emotions or sensations invoked by the original story: the magical feeling of flight in Pan; the chaotic and impulsive escapades of Toad; the nonsensical world of Alice; etc. As such, they offer and represent interpretive experiences rather than literal ones, and thus are both more sophisticated (despite having more primitive animatronics and set pieces) and satisfying.
