They might ask you to stay on for an additional project or they might unfortunately react poorly to your decision. It's best to keep this to the one main reason — you're employer doesn't want to read through a long list of why you hated your job so much.
A resignation letter is not only the first step in making your departure official, it also contributes to the lasting impression you leave on a company. Writing your resignation First and foremost you have to write your letter of resignation.
Read next: Top IT hiring trends for Or, is it time to move on? Adapt it to your contract — Showing that you have considered the terms in your contract shows that your decision is thought through and it avoids any nasty surprises. This is a great opportunity for you to maintain a positive relationship with your soon-to-be ex-employer, and explain your reasons in a clear and rational way.