Keanu Reeves and good reviews have seldom gone hand in hand. Despite a daringly eclectic résumé, and having worked with leading directors these past 20 years, he has more often been an object of derision than acclaim.

He had an especially trying time attempting to throw off the stoner image he perfected, seriously, in River's Edge, then comically in Bill and Ted's Excellent Adventure (1989) and Bill and Ted's Bogus Journey (1993). He has said: "I used to have nightmares that they would put 'He played Ted' on my tombstone."

More recently, Reeves has been earning positive industry comment, starting with his comical turn in Something's Gotta Give. In Constantine (2005), he was convincing as a supernatural detective opposite Rachel Weisz, and also won plaudits for his cameo in the indie hit Thumbsucker. In 2006, he played another undercover cop, albeit a futuristic one, in Richard Linklater's adaptation of Philip K Dick's A Scanner Darkly, which was also well received.

His latest cop role is in Street Kings, co-written by LA crime writer James Ellroy. A treatise on corruption within the LAPD, Reeves plays a detective whose idealism is challenged by the ethically murky waters of his job. The Hollywood Reporter raved: "The film has one of Reeves' best performances: concentrated, grave, a little sad and more than a little demented."

Street Kings was conceived as a vehicle for Reeves, and its director David Ayer admits he was "intrigued" that Reeves should seek out such a role. "The immediate challenge for me was how do I make this light, thoughtful, private, quiet guy believable as a violent, experienced, cynical, dark soul?"

Does he think now that that Reeves' acting is unfairly maligned? "I really do. People's idea of who Keanu Reeves is as a man is fiction, it's based on roles he's played over the years. And you realise how much he is acting. Once I met him and saw who he really was, I was like, 'OK, he can do this, absolutely'."

Reeves trained hard, shot guns and fought people to get in physical and mental shape for the role. "Actual fighting, not Hollywood fighting," emphasises Ayer. "I was like, 'Please don't let his nose get broken before we shoot'."

Given his propensity for playing policemen, does Reeves have any thoughts on gun control?

"You mean should citizens be able to have a weapon? Yeah, why not? I am not fundamentally against citizens having access to a weapon, but I think that it has complications, the use of it. It's probably not the wisest thing. Personally I don't own a weapon."

So what sets this cop movie apart from the others in this cluttered field? "He has created this genre with so many different voices in it. All of these different characters are allowed to be without anyone judging them. They have outcomes, but I think David allows more of a complexity to involve all these different characters and threads as opposed to just having one milieu. In LA Confidential, you get an archetype, there's this kind of 'us and them', but this one has a little more grace. It's more sophisticated."

As in Constantine, Reeves relishes the role of antihero. "They are good to play. What are they looking for? What do they want? Sometimes what they do is heroic or comes with a price or sacrifice or, maybe the way they do it isn't so great. That's when they become an antihero. But that journey with that story is, done well, worthwhile."

Reeves, in person, is all of those things described by the Hollywood Reporter – concentrated, grave, a little sad. Indeed, given the horrific personal grief that Reeves has suffered, it is a wonder that he continues to immerse himself in parts suffused with tragedy. He was devastated by the death of close friend River Phoenix in 1993, and by his sister Kim's long battle with leukaemia. Six months after the release of The Matrix, the baby he was expecting with Jennifer Syme was stillborn. The couple separated soon after and in April 2001, Syme died in a car accident. "I think, after loss, life requires an act of reclaiming," he said. "Grief changes shape, but it never ends. Life has to go on."

Reeves's early life was not much happier. His Hawaiian-Chinese father abandoned the family when Reeves was four and his bohemian British mother raised him and his two sisters in Toronto. At school, Reeves was something of a loner, and did not excel academically. At 14, however, he discovered acting and started doing commercials and bit parts on TV shows before his break in 1986 in Youngblood.

Point Break in 1991 – still a cult favourite – made Reeves famous. And Speed, in 1994, made him a proper box office star. He had to wait a few years for the next bump in his career, but the Matrix trilogy was worth it. The Wachowski brothers' franchise made Reeves one of Hollywood's richest men thanks to a profit-sharing deal; estimates put his income from parts two and three at up to $330m (£155m).

But there are no grieving, tortured souls upcoming on film. He recently finished a remake of the 1951 sci-fi classic The Day the Earth Stood Still with Jennifer Connelly. And next he films The Secret Lives of Pippa Dee opposite a plethora of attractive women: Robin Wright Penn, Winona Ryder, Monica Bellucci and Julianne Moore.

On a personal level, rumours have linked him with indie queen Parker Posey. He did recently buy his first home in LA, having lived at the Chateau Marmont Hotel for years, but is an admitted loner. This, he says, is part of his professional M.O. "I do tend to isolate a lot with my work. I find it helps me and it's a good way to keep a consistency."

Ask him to pick a favourite film and his choice is telling. He announces, "Today I'll pick Little Buddha", in a rather self-important tone suggesting he has a slew of masterpieces from which to pick. Why that one? "For me it was about working with [Bernardo] Bertolucci and [acclaimed Apocalypse Now cinematographer Vittorio] Storaro, and playing a role that I could not possibly have imagined I'd be playing. I went to Bhutan and Kathmandu and that whole experience was life-changing. I was introduced to a philosophy, a religion, a way of being, that I hadn't been exposed to before. The nature of some of the beginning or pillar tenets of Buddhism: permanence, some sorrow, just being in the moment how you are. It was a revelation to me."

Reeves' Siddhartha is a classic loner in the film, albeit one whose isolation is through birth. He says now he does not want to comment on Tibet's current unrest and emphasises that he is not a Buddhist. "But the idea of compassion is pretty good."

Recently, a paparazzo photographer has been attempting to sue him, claiming Reeves hit him with his Porsche. He says he's not surprised at the public obsession with celebrities. "I get it. I mean I want to know things. But I like to keep my personal life private and I think also for me it's better that way for the work we do. I want someone to watch a film and I want them to relate to the character. I don't want their perception of my life to get in the way of that."

And unlike Renee Zellweger – who says she fled Los Angeles because of the paparazzi – Reeves is going nowhere, painful memories notwithstanding.

"It's a wonderful city. I really enjoy it here. It's sunny California. The only thing is, I wish you could see more stars at night."

'Street Kings' opens on 18 April