It was a good, strategic shot. But, in technical terms, it was a horrible drop shot. The first bounce was halfway up to the service line. The second bounce landed almost a foot beyond the service line.
I think it was the right move at that point in the match. Was it an amazing drop shot? no....I've seen her hit better. That being said, when you hit as hard as Maria, you don't really need a great drop shot, you just need one that gets over the net and surprises your opponents