It is a methodology to develop software quickly. It has some good things about it. But it can be very heavy on meetings and agile idealists are not very flexible. As many of the other comments say, a mixture of agile and some other methodology or starting with agile and developing your own process that works for your team or project is the best way of managing a project.
I don't understand why so many people don't seem to write requirements when using agile. Even with agile I will not start coding until I have relatively clear requirements. It is not too bright to start speculative development without really knowing where you are going. https://agilemanifesto.org/