that showing too much emotion in Darcy would have looked out-of-character for him!

If I look at the scene wihtout any reference to the text, I like it better- Darcy seems misty with tears, and Lizzy is oh- so happy!

But, I remember reading somewhere in the archives that engaged couples were given much freedom in the Regency era. So, a little kiss, and hand-holding would not have been too far out of ettiquette.
Moreover, Darcy, with all his suppressed desires at last fulfilled, would certainly have shown his emotions as openly as JA intended!