If you don't already know, this is a series of 3 trilogies, NINE books. So you're making a commitment to read the whole series...and I didn't make it.
If I was rating solely on the first trilogy this would be a five star review. A little slow moving at first, but the story was an amazing mix of social commentary, romance, family drama, all set in the last years of the Victorian era (the book covers Victoria's funeral). If you love Downton Abbey, or big family sagas with tons of characters, or turn of the century England, this is your series. The main plot revolves around the loveless, hopelessly mismatched marriage of the main character Soames Forsyte, a cold, emotionless businessman and Irene-a loving and free spirited musician.
Unfortunately, after book 4, The White Monkey, I give up. By Book 4, we are on to the next generation, with the main character being Soames' daughter Fleur. And this is where things go wrong. I'm not too proud to make the obvious comparison-if it was Star Wars, book 4 would be The Phantom Menace, and The White Monkey is exactly that level of boring and bad. There simply is hardly any story, and Fleur is a terrible character. In the introduction, Galsworthy says that Irene, one of only two major female characters, from the first trilogy is "never...present except through the senses of the other characters, is a concertion of disturbing Beauty..." In other words a deliberate choice to keep her vague and undefined. After spending an entire novel primarily focused on Fleur, I can find another reason....Galsworthy can't create good female characters. At all.
So I skipped over to the Goodreads page for Book 5, and the reviews there seem to be a consensus that it's Attack of the Clones-more Fleur all the time, and little or no plot of consequence. I'm just not interested so I'm stopping here.
I do wholeheartedly recommend the original trilogy. The rest you can skip.