Everybody knows KARAT is spelled with a K. When it's referring to gold, that is. Why I chose to spell it with a C will be a mystery forevermore.
Four people with the first name Johnny, with their last name used in a standard phrase. I get the idea, but how does JOHNNYONTHESPOT refer to this? I was looking for places where "Johnny" could be hidden in a black square. That fits better. That being said, the four individuals are all well known, if a little outdated. When you google the name, first up is Johnny Depp, followed by Johnny Manziel (yuck), and then Johnny Cash. So that's one anyway. Johnny Rotten was born John Lydon, but is best known by his stage name.
There are some nice entries in the fill. ONSLAUGHT is excellent, as is 6D: Spanish steps? (FANDANGO), with a nice reference to Rome (ROMA?) there. A hidden capital redeems 14A: Sessions, e.g.: Abbr. (SEN). I also like the clue for 30A: Class with many unknowns: Abbr. (ALG). It's just too bad there had to be so many Abbrs. 37D: Bad name for an anger management counselor? (STU): hah!
1A: Start of a Latin 101 conjugation (AMO): D. Okay, I like Latin as much as any of us, I think. But to start a puzzle off with this sort of ancient (see what I did there?) crosswordese doesn't make us look forward to the remainder. And indeed, there is a lot of crosswordese: AJA (fine album), EDINA (there was a shocking Minneapolis suburb in the Sunday puzzle: Eagan), ADLAI, AMATI, SEGER.
I thought it was funny that UTURN almost made the full turn, crossing URN. You could read it either direction and get the same answer.
I didn't love it.