Psychological thrillers can take audiences on a wild ride through stories and characters. Whereas horror and thrillers often rely on jump scares or adrenaline-producing excitement, psychological thrillers tend to be more subtle. They can leave an impression on audiences long after the credits have stopped rolling, sometimes even making audiences question exactly what they've just seen.

The 2000s produced some memorable but overlooked psychological thrillers, including early works from now-acclaimed directors and actors. Some received mixed reactions but are worth another look, while others were beloved by those who actually saw them but haven't built the same reputation as other films in the genre. Still, these underrated psychological thrillers from the 2000s are unsettling and worth watching, thanks to their creepy characters, tense atmospheres and, above all, clever plots.

10 'Willard' (2003)

Directed by Glen Morgan

In Willard, the awkward and lonely titular character (Crispin Glover) befriends a group of rats living in his late father’s run-down mansion. When he realizes the rats will do anything he tells them, he uses them to exact revenge against those around him, including his difficult boss. The movie was loosely based on the novel Ratman’s Notebooks by Stephen Gilbert, as well as the 1971 adaptation of the same name.

Willard is an unsettling and disturbing film about loneliness and revenge, which improved on the original by making rats seem even creepier. It can feel slow-paced and over-the-top, but it succeeds thanks in large part to Glover, its greatest asset. He’s great in the role of Willard, from his flustered reaction at mistakenly thinking a coworker is asking him on a date to menacing as he commands his rats to attack his boss.

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9 'Bug' (2006)

Directed by William Friedkin

In Bug, a woman named Agnes (Ashley Judd) begins a relationship with charismatic war veteran Peter (Michael Shannon), who is convinced the military intentionally infected him with a bug. The two hole up in a hotel room in Oklahoma, and soon, an infestation in the room blurs the lines between reality and delusion. The movie was based on the play of the same name by Tracy Letts and was directed by William Friedkin, best known for directing the horror classic The Exorcist.

Bug's final moments are particularly intense—plus the ambiguous ending casts some doubt on how much of the film was real.

Despite some negative reviews, Bug is a great example of compelling small-scale horror dealing with the themes of paranoia and addiction. Its final moments are particularly intense—plus the ambiguous ending casts some doubt on how much of the film was real. Like most of the all-time great entries into the genre, Bug gets more disturbing as it progresses, with Agnes and Peter becoming more paranoid and unsure of their surroundings. The ever-underrated Judd and two-time Oscar nominee Shannon are both impressive in their roles, especially as their mental states deteriorate.

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8 'The Cell' (2000)

Directed by Tarsem Singh

Psychologist Catherine Deane (Jennifer Lopez) has been experimenting with a new form of therapy in The Cell, allowing her to experience what’s happening in a person’s unconscious mind. An FBI agent (Vince Vaughn) convinces her to use her skills to enter the mind of comatose serial killer Carl Stargher (Vincent D'Onofrio) to find his final victim, who’s trapped and still alive. But as she travels deep into his mind, Deane begins to think what she’s experiencing is real.

The Cell wasn’t well-regarded by critics upon its release, although it was a box-office success. Its plot is similar to The Silence of the Lambs but with a sci-fi twist, plus a chilling performance from D’Onofrio as the killer. The scenes that take place in Stargher’s mind are visually stunning and impressively styled, with bright colors and unique costuming and set pieces. Over time, The Cell's standing has improved, with many now considering it among the new millennium's best and most singular sci-fi psychological thrillers.

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7 'The Hole' (2001)

Directed by Nick Hamm

In The Hole, four teenagers at a British boarding school discover and explore an underground hole created decades prior, possibly as a bomb shelter. After the teens go missing for weeks, one of them, Liz Dunn (Thora Birch), turns up and tells her psychiatrist (Embeth Davidtz) that her friend, Martyn (Daniel Brocklebank), sealed her and two others in the hole and left them to die; meanwhile, Martin blames the incident on Liz. The movie was based on the book After the Hole.

The Hole is a clever, well-done film, presenting two very different versions while moving between past and present, with Liz and Martyn presenting their versions of events. As Liz deceives her psychiatrist, so, too, does she deceive the audience, and it’s unclear until the end which version is accurate. The ever-underrated Thora Birch is particularly impressive as the cunning and cruel Liz, at first appearing to be a victim and then showing how menacing she really is.

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6 'Frailty' (2001)

Directed by Bill Paxton

In Frailty, widower Dad Meiks thinks God called on him to kill people revealed as demons. Known as the "God’s Hands," Meiks goes so far as to involve his two sons in his killings. Years later, a man claiming to be one of the killer’s sons arrives at an FBI office and tells them everything he knows. Directed by Bill Paxton in his directorial debut, Frailty stars Paxton as Meiks.

Frailty is a great dark thriller with some ambiguity and twists throughout. It’s unclear if God truly called on Meiks or if he merely thought he was; worst of all, there's a chance he lied about all of it to justify his killings. The movie deals with religious extremism and the ways people can force their beliefs on others, sometimes to violent ends. Paxton’s performance stands out, perfectly balancing a loving father with a menacing murderer. Frailty is a Stephen King-esque film perfect for all those looking for the perfect mix of horror and suspenseful thrills.

5 'Fracture' (2007)

Directed by Gregory Hoblit

In Fracture, successful prosecutor Willy Beachum (Ryan Gosling) is preparing to leave his job for better pay at a successful law firm when his boss (David Strathairn) gives him one last, pretty straightforward case. A structural engineer, Ted Crawford (Anthony Hopkins), admits to shooting his wife, who was having an affair with a police detective. However, Ted represents himself in court and proves to be more than he seems.

Hopkins had already proven he could be terrifying in The Silence of the Lambs, but in Fracture, he delivers another chilling and mesmerizing performance. Gosling is just as good as the prosecutor, playing him as likable yet cocky, and the meticulous, perfection-obsessed Ted can see right through him. The two characters are great to watch as they play off each other, making Fracture an enthralling cat-and-mouse thriller that brings the best out of its two compelling performers.

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4 'Insomnia' (2002)

Directed by Christopher Nolan

Christopher Nolan's Insomnia follows a renowned veteran police detective (Al Pacino) from Los Angeles summoned to a small town in Alaska to investigate the murder of a teenage girl. The main suspect (Robin Williams) begins playing cat-and-mouse games with him. Insomnia is the only Nolan film that he did not write or co-write; instead, Hillary Seitz adapted it based on the eponymous Norwegian film.

While not as well-known and acclaimed as his other work, Insomnia is still an important piece in Christopher Nolan’s career, as it was his last small-scale film before transitioning into blockbusters. Insomnia is a great, if flawed, psychological thriller in its own right, with a memorable performance by the late Robin Williams as the elusive and mercurial murderer. The Oscar winner is suitably creepy and unsettling as he toys with Pacino’s seasoned detective.

3 'One Hour Photo' (2002)

Directed by Mark Romanek

In One Hour Photo, the lonely Sy Parrish (Robin Williams) works as a technician in a photo-developing lab in a mall, with the Yorkin family among his regular customers, bringing film depicting occasions such as birthdays. But after he develops photos proving the father is having an affair, Sy’s idea of the Yorkins as a perfect family comes down, and his already unhealthy obsession with them becomes violent.

Critics praised One Hour Photo upon release, although it hasn’t been as acclaimed as other films in the genre, especially in recent years. It’s a film about loneliness and the all-consuming desperation for connection that can follow. Williams is unnerving as the obsessive Sy, delivering arguably the best performance from his late career. The disturbed character’s insight into the family through their photos makes One Hour Photo creepy enough even before Sy becomes violent.

2 'The Machinist' (2004)

Directed by Brad Anderson

Factory worker Trevor Reznik (Christian Bale) has been struggling with insomnia for over a year, and it’s so severe it impacts his weight and his performance at work. His condition worsens when he unintentionally causes an accident that leads to a coworker (Michael Ironside) losing a limb, and Trevor begins to question his sanity, especially as he starts seeing a mysterious man called Ivan.

The Machinist was praised by audiences and critics alike but has not found the reputation it deserves as a fantastic psychological thriller. It’s an intense, edge-of-your-seat thriller that explores the themes of paranoia and guilt. Anchored by a stellar central performance, The Machinist thrives on the discomfort it provokes. Bale’s performance as Trevor is impressive, and not just because he lost a lot of weight to play the character. The committed and reliable actor digs deep into the character's psyche, elevating the film into the upper echelons of its genre.

1 'Session 9' (2001)

Directed by Brad Anderson

In Session 9, a group of workers takes a job cleaning asbestos out of an asylum that has been abandoned for 15 years—and its history included the abuse of patients and an alleged demonic possession. This infamous reputation, combined with the crew’s grueling work schedule, personal tension and strange occurrences, affects the job, while a former patient’s hypnotherapy sessions play throughout the film.

Session 9 is a thrilling cult classic for a number of reasons, including great character development and original storytelling—even if the basic premise is a pretty familiar one. The movie is also a slow burn that’s brilliant at building tension, thanks in part to the recorded therapy sessions that parallel the events of the film. Along with The Machinist, Session 9 helped cement director Brad Anderson’s reputation as a master of horror and thrillers. Unlike other psychological thrillers of the time, Session 9 hasn't enjoyed a reappraisal and hasn't been rediscovered by younger audiences, keeping it firmly and unfairly in underappreciated territory.

NEXT: The 40 Best Psychological Thrillers Of All Time, Ranked