Your official Graduate Institution Score Report, received by your designated recipients, will include your name, address, email address, phone number, intended graduate major, GRE test scores and associated percentile ranks. It will not include any information concerning the other score recipients you have chosen. Additionally, institution score reports include only the scores that you selected to send to them using the ScoreSelect option. There will be no special indication if you have taken additional GRE tests. See a sample Graduate Institution Score Report .
It should not sound over enthusiastic, though. Professional tone needs to be maintained. Generally, it is not a norm to write anything negative about a person on such letters. However, you can mention a few critical things, if required, so that the letter looks authentic. Recommendation letter, like other formal letters, should include date, place and time. It should have a small introduction part, stating purposes of writing the recommendation letter. Generally, professional reference letters come in 1-page length. But, it could be maximum 2 pages in terms of length.