First off, it's a bit informal and abrupt. Then when you tack on the exclamation point, it just gets annoying. "It's a bit jarring right off the bat — like someone is shouting at me," Schwalbe ...

Dear [first name], ...' Again, it's not the worst greeting in the world, but it's a little old-fashioned. 'Dear Mr./Mrs./Ms. [last name], ...' The "Dear" family is tricky because it's not always ...