Was the real Nell Gwynn as interesting as the character in this movie?

Yes, Nell Gwynn was outspoken, clever, witty, and bawdy, and the king loved her pretty much for all of his life, though he did have lots of other mistresses.

One famous story about Nell is that the king had another mistress at the same time, a Spanish Catholic woman whom the people pretty much hated. The story goes that Nell was riding in her carriage and it was overtaken by an angry mob who thought she was the other mistress and were shouting rude things, particularly calling her a "Catholic whroe". Nell stuck her head out and shouted, "Nay, nay, good people! Be civil, for I am the Protestant whore!"

Nell was well-loved by the public, as well as the king. Even the Queen seemed fond of Nell. :)

She was everything a man could want in looks and personality, plus she was a kind person. She had a hard upbringing, then when she went on the stage after they started allowing women, she soon became the mistress of Charles ll. She had a wicked sense of humor-- that was one reason Charles loved her. She kept him laughing. Her rival in the theatre, at first, was Moll Davis. She also became Charle's mistress, but by that time Moll and Nell were friends so no hard feelings.

I love that period of English history and have read many books about Charles, Nell, etc.

One of King Charles's last thoughts on his deathbed was of her - he entreated
his courtiers to "let not poor Nellie starve".