“Blackfish” was one of the biggest — if not the biggest — documentaries of last year. Its story about a killer whale named Tilikum made a huge impact upon release, and has caused countless people, including many celebrities, to reconsider the viability of keeping killer whales in captivity for our entertainment. The film also earned director Gabriela Cowperthwaite an Oscar nomination.

SeaWorld has yet to recover for the impact of the negative press: in the first quarter of this year, the company reported a 13 percent drop in attendance, as well as lower stock prices — although of course, they claim it has nothing to do with “Blackfish.”

The film takes a radical, emotional approach to the issue of captive whales. The main character of the story is the killer whale Tilikum, a SeaWorld performer captured in the wild and separated from its mother at a young age. Tilikum, who currently resides in SeaWorld Orlando, is responsible for the deaths of three different people, two of whom were trainers.

Killer whales, it seems, are remarkably complex creatures. They have highly nuanced brains and in nature, they form tight-knit social groups that are distinct from each other in ways that still astound scientists.

But take these massive, intricate creatures, put them in captivity and things don’t go over well, as the story goes in “Blackfish.” SeaWorld has tried its best to treat the whales well: it has rigorous training programs for the people who handle the whales, and do everything they can to make sure the whales are in good shape, including, as they recently admitted, giving them psychoactive drugs to treat anxiety and depression. Maybe they just weren’t meant to live their lives all cooped up.

So now that we’ve established what the film is about, how does the movie do what it does?

Well, let’s start by saying that “Blackfish” is a horrible movie. Meaning, watching it won’t make you feel particularly great.

But it’s a well-made movie with a strong message that comes across well. It’s entertaining and informative. It’s also a strongly emotional and occasionally uncomfortable experience. Not only do they get you to feel bad for the whales, who, in addition to living in tight spaces, are often separated from their families at a young age. They also discuss the human deaths in painful detail.

Most of the film consists of archival footage of whales at SeaWorld. The only original footage comes from interviews with former SeaWorld trainers who have distanced themselves from their former employer and are now speaking out against SeaWorld’s handling of killer whales in captivity.

“Blackfish” is an emotional film. And it hits hard. However, viewers can’t help but be a bit leery of the one-sided movie approach.

In other words, you know how you feel when you watch “Blackfish,” but I’m not quite sure what to think.

From the perspective that killer whales should be free, it’s a strong argument, and hard to disagree with. Killer whales are complex animals with complex psyches and it’s difficult to imagine that they belong in such a small space. The emotional and occasionally violent actions of the whales illustrate that.

SeaWorld’s voice, despite having such a huge role in the movie, is completely unrepresented.In fairness, according to the film’s credits, the company declined to be interviewed for the film.

It’s unclear how much the filmmakers actually pressed the company for an interview, but with SeaWorld not offering their take on the issue, It feels like a huge portions of the puzzle is missing.

It would have been especially nice to have heard from current trainers, to learn what they think of the whole thing.

Additionally, it feels like the film doesn’t quite do the trainer that was killed, justice. It’s a depressing movie, and uses her death to convey its message, which works to a degree. One can’t help but ask how the trainer would feel about her death being used against SeaWorld. We can’t know, obviously, but it’s an important question. Would she agree with the film’s message and call it justice, or would she disagree and side with SeaWorld?

Regardless of all of this, the film does succeed extraordinarily at an emotional level. “Blackfish” is a tragic film — both from the whales’ perspective and the humans’. The pain of the whales, and the horror of the innocent people killed, are enough for most people to rally against SeaWorld. Especially considering that, in the wild, there have been no known cases where killer whales have killed any people, and in “Blackfish,” we bear witness to three.

In the end, “Blackfish” is less a film and more a device for change. It’s emotional, and it hits hard. It would be hard to watch it again not because it’s a bad movie, but because it’s a painful one. It may be missing some pieces of the story, but if you have a heart, you’ll be moved by its conclusion.