The Grammar-Translation Method (GTM) is not a set learning style which can be taught or instructed and as such the main goals of it are often overlooked. It is a descriptive rather than prescriptive method which concentrates the focus of learning on a teacher led experience with the student learning language rules and vocabulary.
The main critique of the practice is language development is based on rote memory rather than cognitive progression. Language rules are often difficult to understand without understanding the mechanism for why the rules were created. The English language is particularly difficult to understand the nuances of language. Something as simple as "'i' before 'e' except after 'c'...". Simply translating words from one language to another and attempting to reconstructing useable language skills is difficult.
The learning of words and language rules before speaking slows down the thought process because the speaker has the words and then must think about how to put them into place. On the other hand, many argue that the manner of speaking should be taught before the specific words are taught. This allows a speaker to learn language rules as they become necessary to understand. Languages with various masculine and feminine forms, such as Spanish can be confusing when a new speaker memorizes the rules without putting it into place. The person must decide which rule to utilize, then the proper words before constructing a sentence. However, someone who understands how to speak one gender can attempt the second way and be corrected, thus learning how to properly approach the situation.
When reviewing how most people learned their primary language it was through trial and error rather than memorization. You would ask for water when pointing at food your parents would correct you and say "food". Learning would occur and such is repeated throughout life.