I have seen those who insist that while it's fine in social media and suchlike, the exclamation mark should never be used in 'proper' writing. I disagree, although I do use it very sparingly, saving it for those occasions when it will have most effect.

Take the case of a woman arriving home early to find her husband parading in front of a mirror dressed in her finest lingerie. I would bring out the exclamation mark to round off her response, which is,

"George!"

In that scenario, the woman's outrage is expressed more forcefully with the exclamation mark than it would be with a mere full stop.