FlyThrough

using UnityEngine;

[RequireComponent(typeof(Camera))]
public class FlyThrough : MonoBehaviour {

    public Vector2 moveSensibility = Vector2.one * 15f;
    public Vector2 mouseSensibility = Vector2.one * 2f;
    public float shiftMultiplier = 3f;

    private float vertical { get { return Input.GetAxis("Vertical") * moveSensibility.y; } }
    private float horizontal { get { return Input.GetAxis("Horizontal") * moveSensibility.x; } }
    private float mouseX { get { return Input.GetAxis("Mouse X") * mouseSensibility.x; } }
    private float mouseY { get { return Input.GetAxis("Mouse Y") * mouseSensibility.y; } }

    private void Update() {
        var movement = transform.forward * vertical * Time.deltaTime + transform.right * horizontal * Time.deltaTime;

        if(Input.GetKey(KeyCode.LeftShift) || Input.GetKey(KeyCode.RightShift))
            movement *= shiftMultiplier;

        transform.position += movement;

        transform.Rotate(Vector3.up, mouseX, Space.World);
        transform.Rotate(transform.right, -mouseY, Space.World);
    }

}