In the books, Juha is a somewhat loveable anti-hero. A person who does bad things (alcoholic, violent, ill-tempered, neglecting the law), but you still get the feeling that he has a good heart and good intentions, and he's witty and funny overall. You cheer for him and you hope that he'll have a happy ending, and that he learns from his mistakes and you know that he'll become a better person.

The movie Juha is just miserable and poignant. There's nothing fun about him, nothing charming. You don't believe anything good will come his way for a second. Just depressing.

The books are fun, the movie makes you feel bad. They completely missed the point and failed miserably.

Both the novels and the movie use an unreliable narrator. Difference is that book-Juha is that cooler older brother who tells fun stories about his adventures and you don't even really question if it really happened, you just love hearing the stories. Movie-Juha is that old drunken uncle who always tells the same stuff and you just know it's bs.