In the film, "Star Trek Generations," Data finally installs the emotion chip he retrieved from Lore (Star Trek: The Next Generation, "Descent, Part II," Season 7, Episode 1), and experiences the full scope of emotions. These emotions proved difficult to control and Data struggled to manage them. By the events of "Star Trek: First Contact," Data gained complete control of the chip, which included deactivating it to maintain his performance efficiency.
I like how every time Data does something completely cool and everyone in the background on the bridge -who once had smiles upon their faces- slowly stare at him in astonishment and weirdness. Their smiles slowly fade as they witness him in his natural habitat.