"Justice League" was hit with some Kryptonite at the box office this weekend.

The mashup that brought together some of DC Entertainment's biggest superhero stars, including Batman, Wonder Woman, Aquaman, Cyborg and the Flash, nabbed an estimated $94 million at the box office in North America this weekend.

That number, while still big for an opening weekend, came in under the roughly $110 million the industry expected. It's also the lowest opening for the Warner Bros. superhero brand, trailing films like 2013's "Man of Steel," 2016's "Batman v Superman: Dawn of Justice," 2016's "Suicide Squad" and this summer's "Wonder Woman." It is the only film in the DC Extended Universe to not crack the $100 million mark in North America at its opening.

The film brought in $279 million worldwide.

The sluggish opening for the film, which stars Ben Affleck as the Caped Crusader and Gal Gadot as Wonder Woman, is a bit concerning for Warner Bros.

"Justice League" was designed to be the apex of the DC Entertainment connected universe of films, as it brings together all of the brand's biggest heroes.

Related: 'Justice League' looks to its biggest heroes for box office success

So what went wrong? Bad reviews could be a culprit.

"Justice League" holds a 40% score on the review site Rotten Tomatoes. That's a steep drop compared to the brand's biggest hit, "Wonder Woman," which nabbed a 92% score in June.

Critics called the film a "big, ugly mess," saying that superhero fans "deserve better."

By comparison, the film appeared to win over more of the movie going public. It received a "B+" on CinemaScore.

The sluggish debut for "Justice League" caps off what was otherwise one of the strongest years for superhero films. The genre nabbed both big sales and strong acclaim.

Films like "Logan," "Guardians of the Galaxy Vol. 2," "Wonder Woman," "Spider-Man: Homecoming" and "Thor: Ragnarok" were all hits with audiences and critics alike.

(CNN, like Warner Bros., is owned by Time Warner (TWX).)