It seems common enough that artists are often far less interesting then their art when it is good. A great deal makes sense when this is examined.
But it is a particular risk of an artist that someone else might try and make art of their life. What seems to have happened here is the expected dilution.
This man made two extraordinary films early in his life: Tempest and Jubilee. Both of these, incidentally featured Tonya Willcox, a profound presence.
Later in life, he turned himself into his own performance, and thus became dull. Tonya was replaced by Tilda Swinton who would herself do some profound things — but not in a Jarman film.
Then in further dilution of power, this life is turned into a film, created and narrated by Tilda. The rough shape of it her offscreen narration while she intensely looks at the camera from London streets. The message is that Derek was a true prophet of the unprocessed truth. This is interspersed with filmed interviews of the man and shots of the decorated cottage where he spent his last days.
The film itself is sensible and direct. It carries an obvious truth. It is well made. We know when it and his life will end, and they both end gracefully. None of these things are true of a good Jarman film.
Ted's Evaluation -- 1 of 3: You can find something better to do with this part of your life.