Woody, Buzz and Jessie are returning nine years after they said goodbye to Andy and settled into their new home with Bonnie at the end of Toy Story 3.
The Hollywood Reporter's Todd McCarthy said: "It's now certain what one of the summer's blockbusters will be.
"More than that, how many other film series can legitimately claim to have hit four home runs in a row?" he added.
Variety's Peter Debruge said the movie gives "satisfying emotional closure", adding that "the fourth movie wraps up the saga beautifully".