I like this movie, I like the actors but the chemistry

Ben Whishaw is an excellent actor. Arguably the best actor working today. He's in a class by himself. But he is not who most people imagine as a romantic hero. In this case he was So Perfectly Cast. Keats himself was a small man, no taller than 5 foot. But more important than physical structure Whishaw captured Keats' strengths and weaknesses in such a powerful balance.

However, I have to dispute your opinion of Abbie Cornish as Fanny Brawne. She is a wonderful actress and brought a lot of depth to her character. She effortlessly evolves Franny from a frivolous rather out spoken but sheltered young girl, through her obsessive flirtation, to a strong willed, strong spirited woman in love. Maybe you need to re-watch the film from Franny's perspective.

Anyway, I think perhaps there are people who allow their presupposed expectations of what a female romantic lead would look like to overwhelm their opinion. Perhaps you expected a frail looking actress instead of Abbie. However, whatever she is in, I prefer Abbie Cornish because her performances are always so excellent.

"I'd never ask you to trust me. It's the cry of a guilty soul."