If I'd seen Top Gun: Maverick without having seen this film a few weeks earlier I might have been shocked at how weakened and elderly Val Kilmer looked. That was until I realised that he, like the unnaturally and eternally youthful Tom Cruise, is now in his 60s and has – as he explains in this movie about his life and times – been through treatment for cancer in his throat that's mostly destroyed his voice.

He was a pretty titanic presence in Hollywood from the late 80s to the mid 90s before the stories about how impossible he was to work with finally caught up with him and derailed his career. So now, whether it's an act of penance or just a case of life not being fully examined until it's through a lens, this is the least hagiographic autobiographical documentary film you've likely ever seen.

Not because it shows or attempts to explain Kilmer's infamous reputation, but in just how ill and spent he looks. At one point, asking for a break from a booth signing autographs at some con or other, he gestures urgently to a nearby rubbish can, sticking his head into it to vomit violently when his assistants and hangers-on pass it to him.

He didn't direct this film but he's listed as a producer, which means he was either the driving force behind it or bought completely into the vision of what it would be, and it's to his credit that it shows him in such a state today.

As is soon apparent, Kilmer's had one of those lives where there was always a video camera around, usually wielded by him as he documented everything from family get-togethers to what went on behind the scenes on film shoots. One of the most charming moments is when he approaches a rotund Marlon Brando, stretched out on a hammock on a Queensland verandah while filming The Island of Dr Moreau , the late actor asking Kilmer to 'give me a shove' so the hammock rocks a bit.

The narrator, who sounds for all the world like Kilmer, is actually his son, the script revealing so a little of the way in, and it traces his whole life. He grew up in suburban Los Angeles, his early life marred by tragedy when his beloved brother – with whom he made home movies – drowned in an outdoor jacuzzi after an epileptic fit.

He eventually goes to New York to become an in-demand stage actor, working his way up to performing with some very big names, even at one point getting two of the stars he's an understudy for (Kevin Bacon and Sean Penn) to moon the camera for him. But screen stardom comes rapidly in the late 80s and it's fun to see an inside look at what the rest of know about his career since.

He initially wasn't terribly interested in Top Gun, considering the script a bit 'silly'. He signed on to do Batman Forever without seeing a script and before there was a director because – as he reasoned – what grown man with a little boy inside him wouldn't want to play Batman? It was only during filming that he realised how stupid the whole thing was going to be and how unworkable the batsuit was (he couldn't hear a thing in it).

And all while he's off on adventures filming movies, falling in love with Joanne Whalley and having two kids with her, being handed divorce papers while on the set of The Doors because of how much such a demanding role took him away from his family, he's filming it all.

It's interspersed with every personal detail Kilmer considers important about himself, from the aloof mother he idolised, his parents' divorce, having to sell his beloved parcel of New Mexico land to get his father out of trouble after a bad investment and of course, his battle with his health.

There's an almost perfect ratio of personal to professional context, all of it informing the other, and the assembly of all the material he and his directors had to choose from and the narration he wrote for it is as raw a personal history as you're likely to see. If you'd written Kilmer off years ago as a spoilt tinseltown brat, this will remind you there's always a human being behind the facade.