Tenerife still boasts some places of great natural beauty which are almost completely off-the-radar, such as the forgotten village of Batan. But most areas of potential touristic interest have long since been "discovered". Many of these are still must-see despite the crowds, like the Roques de Garcia. But some of them are like Los Gigantes: over-run, obnoxious places you'd do well to avoid.
Generally, any whale-watching trip comes with a massive disclaimer: there's no guarantee that you're going to see whales. But the guys from Third Element were either recklessly confident, or the sightings between La Gomera and Tenerife are just that dependable, because they said we'd "definitely" spot some pilot whales, along with bottlenose dolphins.