The Aerial Tram on the Atlantic side, near Braulio Carrillo NP, was interesting. It was a little expensive at $55 per person, plus $10 each for the serpentarium and the butterfly garden. The latter, you should skip. There are better serpentariums and butterfly gardens around Costa Rica, actually, like the ones at La Paz Waterfall Gardens. The Aerial Tram is unique only because you are riding a tram. But if you are planning on doing Ziplines anyway, then you can skip this. On the tram, we didn't see any animals except butterflies and moths. People usually get split up in groups up to 6 per group, with a guide who either speak English or Spanish. There were 3 in our group so we were grouped with another family who happen to be Spanish only. Our guide split his time repeating his talk in Spanish and in English. We understood some Spanish but not a lot, so basically there was a lot of talk and not enough time for silence when animals can come out. With the way it was set up, I don't think you can spot any animals. We saw birds, hummingbirds, and a sloth in line when we were waiting for the tram but not ON the tram.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.