How different is the BBC's Little Women from Louisa May Alcott's original novel?

The novel has been adapted again and again, from the first silent movie a century ago to the beloved 1994 film starring Susan Sarandon, Winona Ryder, Kirsten Dunst and Claire Danes. The BBC has also adapted the novels as a serial three times before.

And now, starting on Boxing Day, Call the Midwife creator Heidi Thomas has turned Little Women into a three-part drama to bring the story to a new audience.

Is the BBC's 2017 Little Women faithful to the original novel?

Thankfully the drama stays true to the spirit and the plot of Louisa May Alcott's most famous novel in this loving adaptation. When the story opens, it is Christmas Eve and Meg, Jo, Beth and Amy March are bemoaning their lack of Christmas presents – with the first lines of the first chapter almost perfectly recreated as a homage to the original.

Over the next three hours we see the sisters go through much heartache, joy and romance as they grow from childhood to adulthood: there is birth, death, marriage, rejection, loss, and by the end so much has changed – even if the sisters' love for each other remains the same.

But with just three hours to play with and so much material to get through, Heidi Thomas has had to distill the story down to its essence and take an axe to some of the more fanciful and less plot-driven scenes. Luckily she has been wise enough to preserve all the key moments that readers will remember no matter how many years have passed since they last picked the novel off their bookshelf.

So – [and of course here come some SPOILERS!] – We have the introduction of boy-next-door Laurie Laurence. We have Jo refusing to let Amy accompany her to the theatre, and Amy burning her book in retaliation. We have Amy's dramatic fall through the ice. We get that awful moment when the telegram comes and Mr March gets injured in the American Civil War, forcing Marmee to abandon her girls and rush to his side. And we have the defining moment of Little Women, the one that has made millions of girls cry into their pillows and left Friends character Joey Tribbiani so upset he had to put the book in the freezer: Beth dies.

But what's not there? What has been left out?

One of the backbones of Little Women is John Bunyan's The Pilgrim's Progress, a Christian allegory from 1678. The March sisters construct the framework for their own narrative using this story, which guides them on their moral mission to be better people. Each sister declares what their "burden" is (a quick temper; vanity; shyness; selfishness) and the stages of the story are marked by their journey as "pilgrims" together. Their "game" begins when they are still children and helps to guide them into adulthood.

But we live in a more secular age, and much of the religious content of Little Women has been laid aside. Probably wisely, this includes The Pilgrim's Progress: the story survives perfectly well without it, and few people know the ins and outs of that narrative any more.

More generally, Heidi Thomas has scaled back the preachier, more godly aspects of the book: all those musings about Jesus' love and Marmee's religious moralising. For example, when – in the TV drama – Marmee hides four little leather-bound books under her daughters' pillows on Christmas Eve, you wouldn't necessarily even know they were meant to be bibles. I had forgotten until I looked back at the novel, where we read how the girls wake up in the morning to discover their presents and then snuggle up in bed to read the Word of God together.

Lest some complain, religion in still there in the story: how could it not be, in such a religious age? As Beth lies suffering from scarlet fever, Jo promises to devote her life to God – if only her sister will get better – but if she dies she will struggle to believe how God could be so cruel. But there's less of it, and it's less about instructing the reader or viewer, too.

Also missing is some of the more fun, meandering, less plot-driven material – including the Pickwick Club, which meets so merrily in the novel, and all the girls' amateur dramatics. We don't see the family newspaper, or the bird-box for letters – both of which were included in the 1994 film. These things are sad losses, but Little Women survives without them.

Are the characters true to the original novel?

Yes – largely. The main difference is that, when the story starts, the March sisters are meant to be 17, 15, 13 and 12 – but in this adaptation they are played by young adults, and it shows.

In the 1994 version "Young Amy" was played by cute little Kirsten Dunst and was then "aged up" when Samantha Mathis took over the part, making it much less creepy when [spoiler alert] Laurie fell in love with her. But Heidi Thomas has made a bold decision to keep the same actress all the way through, and has opted to have a 20-year-old play a child who is not yet even a teenager.

Now, Kathryn Newton does a terrific job of playing the littlest March kid, but she looks the age she is, and at the beginning of the story that is a problem (though not at the end!). In the novel, Amy starts out with the wide-eyed innocence of the indulged child who yearns to impress her friends with pickled limes; she endears herself to the reader with her love of trying out long words in sentences that don't make sense, and her selfishness and lack of self-awareness is that of a little girl. That is why we forgive her silliness.

But by seeming older in the TV version, this Amy is much, much less likeable. Her childishness is unnatural. She burns Jo's book in such a knowing way and with so much malice – feeding the pages into the fire and petulantly refusing to be sorry – that, while Jo might forgive her in the end, the viewer won't.

Talking of Jo, Maya Hawke is spot-on as everyone's favourite tomboy and aspiring writer. Meg (Willa Fitzgerald) is very pleasing as domestic and motherly with her yearning for luxury and her pride in her looks, and Beth (Annes Elwy) couldn't be more exactly how she is in the book.

The danger in casting and writing the character of Beth would be if she was so perfect and selfless that she crossed over into being irritating. But this Beth, with her freckled face and dreamy eyes and quiet reserve – with her musical talent and shy friendship with Mr Laurence – will break your heart all over again.

Emily Watson is, of course, Marmee through and through with her wise face and secret smile, and Michael Gambon steps in well as Mr Laurence. But if anything, Angela Lansbury actually takes the part of Aunt March and (if we may say so) actually makes her better than in the novel, giving this crotchety rich old great-aunt so much hidden humour and comic timing that you can't help but love her.