Jim Carrey is the movie.
Jim Carrey is one of the great comic actors of the 90's, and this film is one of those that opened the doors of stardom for him. He already worked with comedy before, of course, as an actor and stand-up artist, and he took advantage of this background to build Ace, an animal detective with eccentric habits and manners.
In general, this type of comedy is not to my liking, but I have to recognize Carrey's enormous qualities and talent. In cooperation with director Tom Shadyac (I don't know if it was the first, but there were several throughout their career), the actor did a truly inspired job that gives the film all its strength and originality. Imagining this movie without Carrey is impossible. Sure, there's a lot of exaggeration, and the rest of the cast is driven to exaggerate, trying to keep up with the protagonist's bizarreness, but that's a minor problem, in my opinion.
The film also has good cinematography, which makes good use of the scenarios and chosen filming locations. The pace of the film is quite fast and the feeling that remains is that the film could have gone on longer and a lot of things would have been cut on the editor's table. For me, the great weakness of this film turns out to be the script, involving the sudden disappearance of the mascot of a baseball club – a dolphin. The strength of the protagonist actor and the originality of his character end up transforming the whole story into a detail without much force, a mere pretext for Carrey to do all that.