Enthusiasm in Reference Letter
It's once again LOR season and I've been writing a bunch as well.  I don't think it's so much a question of finding the right language as it is how you present your case for recommending the student.
I'm not sure if you'll find this directly responsive, but here's how I think about it.  I expect the reader has no idea who I am or what my standards are.  I need to give as much objective information about my relationship with the student and their performance as I can so the reader can understand the basis for my judgement and can decide for themselves whether they agree.  That starts with the classes they took with me or the semesters I hired them as staff and their duties.
Sometimes, I don't know much about the student except their grade in my class (which the reader will already know from a transcript.)  An example would be a sophomore who was in my section in one of our 1000+ student intro computer science courses.  So, I'll describe the class, the assignments, how grading was done, emphasize the difficulty, give the student's final rank and add any additional information information I have, e.g., they were a top participant in our Piazza forum, or at least, that I've discussed the student's plans with them and support them.
Once I give that objective information, then I attest to their knowledge, skills and abilities, suitability for teaching and research, etc., inserting a few superlatives, and give my highest recommendation (assuming I can; if I can't, I try to politely decline) and invite them to contact me if they have questions.
For me, an LOR is usually about one to one and a half pages, including room at the top for the letterhead and inside address, and signature at the bottom.  (Yes, I think it's worth using a letterhead template; it  communicates that you cared enough to put some time into it.  I also think it's worth a signature, but that's just another .jpg in my template.)
By now, it's pretty formulaic for me and I'm usually able to bang out a new LOR in an hour or two.
The really hard LORs to write are the ones where I've known the student for several years, they've been in one of my smaller classes, I then hired them to help me teach it, they've been in my office a ton, they're smart as all get-out, and now I really care about them.  Had one of those a couple weeks ago; I struggled for days how to write the letter he deserved.