So bad.

“Ghostbusters” is a horror from start to finish, and that’s not me saying it’s legitimately scary.

More like I was horrified by what was transpiring onscreen.

How could so many talented, well-meaning artists, who clearly loved and respected the original, produce such a raggedy-looking, thuddingly unfunny, utterly unnecessary reboot?

For months, controversy has swirled around the new “Ghostbusters” movie. The trailer was reportedly the most hated in YouTube history, for what that’s worth (or not worth), which led to some pundits saying some of that hate was rooted in sexism.

Others said the fact the Leslie Jones character wasn’t a scientist and seemed to have a role that called for her to play into stereotypes smacked of racism.

Of course, people were voicing these opinions without having seen the entire movie. Well, I have seen it — and while I believe the concerns about racial stereotypes were overblown, “Ghostbusters” is one of the worst movies of the year for multiple other reasons, including:

Bad acting.

Uninspired directing, editing, cinematography and music.

Cheesy special effects.

A forgettable villain.

A terrible script.

Let’s go ahead and issue the obligatory SPOILER ALERT. Later in this review, I WILL be discussing the nature of the cameos by some of the cast members from the original “Ghostbusters.” You’ve been warned.

The 2016 edition of “Ghostbusters” is not a sequel or a remake per se. While there are multiple visual and musical nods to the 1984 classic (to the point of distraction), this is a stand-alone disaster. (One indication this story takes place in the same universe occupied by the original Ghostbusters: We catch a glimpse of a bust of the late great Harold Ramis’ Egon Spengler character.)

In present-day New York City, Kristen Wiig’s Erin is an uptight academic trying to distance herself from her college days when she and her best friend Abby (Melissa McCarthy) published a book claiming ghosts were real. Erin and Abby are estranged — but they’re reunited via plot device when honest-to-ghostness apparitions surface in New York, creating all sorts of evil mischief.

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Real-life ghostly moments for Melissa McCarthy, Leslie Jones

Wiig and McCarthy co-starred in “Bridesmaids” (directed by the usually terrific Paul Feig, who is at the helm here) and they’re enormously charismatic and versatile screen actors — which makes it all the more disappointing to see them flounder separately and together here. They’re both surprisingly muted and flat.

Then again, better understated than insanely over-the-top, which is what we get from Kate McKinnon as Holtzmann, the “wacky” scientist of the bunch. McKinnon is so good on “Saturday Night Live,” but she absolutely butchers her performance in this film — mugging for the camera, bouncing around in an exaggerated manner as if she’s in a “Three Stooges” short, and drawing attention to herself even when a scene calls for her to react and not engage in wholesale attention-getting thievery.

Jones is loud and unsubtle as an MTA worker named Patty who becomes the fourth Ghostbuster, but I’m not sure there’s a way to deliver lines such as, “Aw, hell naw!” without going big.

There’s very little chemistry between any combination of the four Ghostbusters, who spend a lot of time strategizing about their next move and then saying “Woohoo!” when they hit the streets.

Chris Hemsworth further drags down the proceedings as their receptionist, Kevin, who’s monumentally stupid — but also narcissistic and annoying. Hemsworth tries too hard to be funny, instead of creating a legitimately funny character. (It doesn’t help matters that Wiig’s Erin is so smitten with this dope she can barely think straight around him.)

As for those wildly hyped cameos by original “Ghostbusters” cast members Bill Murray, Dan Aykroyd, Ernie Hudson and Annie Potts — and once again, SPOILER ALERT! They don’t play older versions of their characters. They’re just wedged into the story as irrelevant, plot-stopping cameos. Dan Aykroyd saying “I ain’t afraid of no ghosts” isn’t a clever homage to the original; it’s a self-conscious and cloying wink that serves no real purpose.

The special effects in “Ghostbusters” are so mediocre I’m wondering if they’re a nod to the relatively crude effects of 1984. (Or maybe they’re just not very good.) The ghosts aren’t frightening and they’re not funny and they have almost no backstory; they’re just hissing, hateful, murderous creatures storming through the city.

Neil Casey plays the movie’s main villain, a creepy hotel janitor named Rowan. He’s one of the most forgettable villains of any movie I’ve ever seen. I’m already forgetting his name as I finish this paragraph.

Andy Garcia does what he can with this role as the mayor of New York, who is in deep denial about the whole ghost thing. (It’s a pale imitation of William Atherton’s fantastic work as Walter Peck, the EPA official who tried to shut down the Ghostbusters in the 1984 film.)

From multiple visual references to the iconic logo to a new take on the catchy Ray Parker Jr. (by way of Huey Lewis) theme song to the appearance of some very familiar ghosts to the aforementioned cameos, “Ghostbusters” keeps telling us: Yes, we know we’re revisiting a classic.

Some things are better left alone.

★

Columbia Pictures presents a film directed by Paul Feig and written by Feig and Katie Dippold. Running time: 117 minutes. Rated PG-13 (for supernatural action and some crude humor). Opens Friday at local theaters.