The basic premise is a lot of fun, especially for audiences who are pet-owners, and the creative team took full advantage of exploiting the quirks of each animal in the film. The humor is geared more for the children (I mean, this is a kid's film), and it does slightly go on longer than necessary, but there are some great moments that stand out. One of Illumination's signature trademarks, for example, is having a fantastical, over-the-top dream sequence in the middle of the film. In this one, Max and Duke run into a sausage factory and eat to their heart's content, before they stumble upon a vision of living sausages singing as the two devour them to bits. For adults, this is especially hilarious if you're aware of another animated film about sausages to be released in August, Seth Rogen's Sausage Party.
Seeing Kevin Hart in an animated children's film was very entertaining. He plays Snowball, a maniacal white rabbit bent on revolution and freedom from domestication, with an underground cult in the sewers and multiple followers to boot. Hart really gave it his all for this role, and it was tremendously great seeing him play to humor that was more family-friendly in nature, but still has the edge that he has given it before as a comedian.
The music for the film also creatively stands out. The song selection Illumination uses is great as always, appropriate for each scene. The head-banging heavy-metal poodle always gets a few laughs. On top of this, a brilliant (sometimes zany) score by Oscar-winner Alexandre Desplat fits in perfectly with the city scene, recalling with fond nostalgia moments of Gershwin, Mancini, and Leonard Bernstein.
There is one major flaw with the story disguised within the framework. The plot of the film is highly derivative of the movie which jump-started Pixar's career, Toy Story. How so? The main character and their owner are thick as thieves. A new character is introduced into their lives. Owner loves both, but main character gets instantly jealous of the other one. The two fight until their rivalry forces them into unknown surroundings, far away from home. They must work together to go back home to their owner and their normal lives.
Unlike Buzz and Woody, however, Max and Duke are not given enough time to bond. The pacing of how their relationship grows is all over the charts, mainly due to focusing on the humor and world the animators have created. The start of their predicament feels rushed, whereas their fight for survival and to get home drags on slightly and feels forced (much of which owes itself to Duke deciding to save Max from trouble when there's no buildup as to why). There's a key scene regarding Duke's old owner (which I won't reveal more about) that feels shoehorned in rather than genuine, distracting the two from their main journey.
Ultimately, the elements of The Secret Life of Pets are so well done that these flaws are concealed in the bigger picture. The action is decent, the animation is vivid and colorful (representing New York well), the cast is great (especially Kevin Hart as Snowball), and the characters are memorable. It's no Finding Dory, but it's fun for the family, for children, and for pet-owners.