I don't know if I was just on Roger Barkan's wavelength tonight, but four of the six long answers were gimmes:
1A: You can sink your feet into them (shag carpets)...although I initially thought they were referring to some kind of slippers.
53A: Start of a series (television pilot).
55A: __ diet, food plan emphasizing olive oil, fish, fruit, vegetables and red wine (Mediterranean). This sounds like my kind of eating plan...in fact, that was tonight's dinner.
56A: Gulf war offensive (Desert Storm).
After I had some of the downs in place, I was able to get 12A: Bus line? (step to the rear) and part of 14A: Caribbean cruise port of call (Charlotte Amalie). It's not one I'm familiar with, but I knew Charlotte was the first word...the rest came from crosses.
Other multiple-word clues/answers that I really liked:
17A: Sprinted, perhaps (ran a race).
28A: Comparable to a wet hen (as mad). I had mad as at first but had to think the way they were thinking when they wrote the clue.
32A: Pointed warning? (En Garde). Probably my favorite. There's actually a game by that name!
50A: Major component of kidney stones (uric acid).
14D: Coffee alternative (chai tea). I have to seriously cut back on coffee consumption...heart palpitations that may be aggravated by caffeine. I'm going to try to limit it to just my morning cup. No more iced Americanos in the afternoon. My favorite coffee shop may go out of business. How does chai tea compare caffeine-wise?
12D: It's guarded in a soccer game (shin bone).
31D: Accessories for a secretary (desk set). This was my first guess, but I erased it in favor of something ending in an S. Once I revised 28A to as mad, I went back to desk set. Generally, when I go with my gut it pays off.
Was stumped by 29D: Language of India with a palindromic name (Malayalam). Didn't have a clue...but was able to fill in any letters I got at the opposite end of the word. Here's an article on it.
The first clue I saw was 19A: Early film actress Pitts (Zasu), so that was the first answer I filled in. I then started working in a circle around it. I don't think I've ever done a puzzle in such a random fashion. Good cross at the Z with 19D: Daydreamed, with "out" (zoned).
Liked seeing 26A: Utah's __ Mountains (Uinta), 13D: "Copacabana" antagonist (Rico), and 26D: Major in astronomy? (Ursa). All good words ending in vowels. The one that seemed strange was 1D: Star performer's reward (standing O). I don't think I've ever heard it referred to that way, and I was sure I had something wrong.
I need to be up early for some lab work. I detest 12-hour fasts. I don't normally eat at this hour...but because I can't, I want to. I'll wake up tomorrow and be totally famished. Mind over matter, I know...
Anyway, here's the grid...
...and I hope to see you tomorrow.