I think I basically did the beginning of my novel a shock therapy.
Since my story has too many different elements, fantasy, sci-fi, politics, war, military strategy, in the real world, with angels and demons involved.
I wanted to make it clear from the beginning that there would be a lot of different things together, if they supported it or liked it they would surely continue, if not then at least they would find out quickly that my story was not for them. But at least it would not take anyone by surprise if the characters spoke at some point about the foreign trade policy of the United States and in the next scene look for clues about a lost werewolf in the city.
The beginning of my novel is in the middle of the story, many important events happened before chapter 1. An angel visiting an aircraft carrier heading to war. In it the angel talks to the protagonist about things that happened in the past and explains a little why he is on that ship. It is explained that he is not there trying to support his faction to win the war, but because he is helping the angels to recover an object. In return they will heal his sister's illness. So his priority will not be to win the battle but to steal an object and get out there alive, he only has to act until the right time.
Apparently, it has worked quite well for me, because what they have complained about the most was my grammar. And not so much about the great lack of context that the beginning has. Much of my novel is about revealing what happened in the past little by little, so telling everything that happened just to have the context of the beginning would take a toll on me by releasing the same information later on where it has much more weight. An example would be that what the protagonist sought to recover is a stone that fulfills wishes. But that for some reason he refuses to use it, because there is a price to pay, readers do not know that price. Having told that price would have made him see later where he explains why another character should not use, and because he does know the price to pay it would be less shocking.
I also believe that when opening with a lack of information so that readers want to continue reading to find the answers to those questions.Of course, you better know the answers in advance, because each of those information holes that you leave, is a promise with the reader that at some point it will be answered in a credible way.