How formal should a recommendation be in the US? I am a lecturer in a European university. A student from my department asked me to write a recommendation for a program somewhere in the US that he wants to attend.

I have read the horror stories about American recommendation letters, where apparently "He is not only quick at learning and good at solving complicated problems, but also with a logical and creative mind that enables him to raise some insightful views. I was also deeply impressed with his diligence and outstanding communication ability, compared with my other students." is considered lukewarm(!) and grounds for rejecting the applicant.

I have found a few sample recommendation letters and advice from different universities/people around the internet and I've used them as inspiration to spruce up what I had initially written. I have also asked colleagues, but understandably they mostly write letter for other European universities, where such superlative language would usually be reserved for sarcasm or toadying.

However, one thing that is rarely consistent is how formal the letter should be.  More precisely:


How should I start the letter? "Dear colleagues"? "To whom it may concern"? "Esteemed organizers"? Similarly, how to end it? "(Best) regards"? "Sincerely yours"?
How to refer to the applicant in the letter? "Jane"? "Jane Doe"? "Mrs. Doe"?


I would rather not penalize the student because I do not understand foreign cultural norms.
Formality is the wrong parameter to worry about.  Write at whatever level of formality you are most comfortable writing to your target audience.  (But err on the side of formality, unless you know your reader personally.)

The parameter you should worry about is credibility.  Your readers don't just want to know that you think highly of the student; we want to know why you think highly of the student, and why we should trust your judgement.


  He is not only quick at learning and good at solving complicated problems, but also with a logical and creative mind that enables him to raise some insightful views. I was also deeply impressed with his diligence and outstanding communication ability, compared with my other students


This is not a terrible recommendation letter because the praise is insufficiently strong; it's a terrible recommendation letter because the praise is vague.  Which complicated problems?  How do you know he has a logical and creative mind?   What insightful views?  How did he show diligence?  How and where did he demonstrate his outstanding communication ability?  (And do you mean speaking, writing, or both?)  And why should we trust your judgement at all?  Be specific.

Without these details, this letter looks like flowery boilerplate that could be applied to anyone.  The letter says nothing specific about the student, which makes me think the writer knows nothing specific about the student.  Moreover, the letter says nothing about the writer's expertise, strongly suggesting that he expects to be trusted merely because he's old and tenured.

In short: Show, don't tell.

The "horror stories" page you link to gives similar advice.  (Did you actually read it?)