GameManager of my Unity game architecture

using System;
using UnityEngine;
using UnityStandardAssets.Characters.FirstPerson;

namespace UnityGame.Architecture.Managers
{
    public class GameManager : MonoBehaviour
    {
        #region Fields
        private static Manager[] managers;

        private static GameManager instance;

        private static bool isInGame;
        private static bool isPaused;

        [SerializeField]
        private FirstPersonController firstPersonController;
        [SerializeField]
        private GameObject shooterGameObject;
        [SerializeField]
        private GameObject hudGameObject;
        #endregion

        #region Properties
        public static GameManager Instance { get { return instance; } }

        public static bool IsInGame { get { return isInGame; } }
        public static bool IsPaused { get { return isPaused; } }
        #endregion

        // Use this for direct initialization
        private void Awake()
        {
            instance = this;

            managers = new Manager[]
            {
                new ActorManager(),
                new LevelManager(),
                new GUIManager()
            };

            // Wake all the managers
            foreach (Manager manager in managers)
                manager.Awake();
        }

        // Use this for late initialization
        private void Start()
        {
            // Start all the managers
            foreach (Manager manager in managers)
                manager.Start();
        }

        // Update is called once per frame
        private void Update()
        {
            // Update all the managers
            foreach (Manager manager in managers)
                manager.Update();

            if (isInGame && !isPaused && Input.GetKeyDown(KeyCode.Escape))
                PauseGameplay();
        }

        /// <summary>
        /// Gets the manager of the specified type.
        /// </summary>
        /// <typeparam name="T">type</typeparam>
        /// <returns>The manager in question</returns>
        public static T GetManager<T>() where T : Manager
        {
            foreach (Manager manager in managers)
                if (manager.GetType() == typeof(T))
                    return manager as T;

            Debug.LogError(string.Format("Manager {0} doesn't exist", typeof(T)));

            return default(T);
        }

        public void StartGameplay(string difficultyChoice)
        {
            if (!Enum.IsDefined(typeof(DifficultyType), difficultyChoice))
            {
                Debug.LogErrorFormat("Parse: Can't convert {0} to DifficultyType enum, check the spelling.", difficultyChoice);
                return;
            }

            GetManager<GUIManager>().HideActiveMenu();
            TogglePlayerControl();
            GetManager<LevelManager>().StartLevel(1, (DifficultyType)Enum.Parse(typeof(DifficultyType), difficultyChoice));
            isInGame = true;
        }

        public void StopGameplay(bool isGameWon)
        {
            GetManager<GUIManager>().ShowMenu(isGameWon ? MenuType.Highscore : MenuType.GameOver);
        }

        public void RestartGameplay()
        {
            StartGameplay(LevelManager.CurrentDifficulty.ToString());
        }

        public void PauseGameplay()
        {
            isPaused = true;

            Time.timeScale = 0.0f;
            TogglePlayerControl();
            GetManager<GUIManager>().ShowMenu(MenuType.Pause);

            foreach (Manager manager in managers)
                manager.Pause();
        }

        public void ResumeGameplay()
        {
            isPaused = false;

            Time.timeScale = 1.0f;
            TogglePlayerControl();
            GetManager<GUIManager>().HideActiveMenu();

            foreach (Manager manager in managers)
                manager.Resume();
        }

        public void QuitGame()
        {
            Application.Quit();
        }

        private void TogglePlayerControl()
        {
            ResetCursorPosition();
            Cursor.visible = !Cursor.visible;
            hudGameObject.SetActive(!hudGameObject.activeSelf);
            firstPersonController.enabled = !firstPersonController.enabled;
            shooterGameObject.SetActive(!shooterGameObject.activeSelf);
        }

        private void ResetCursorPosition()
        {
            // Both resets and locks the cursor position
            Cursor.lockState = CursorLockMode.Locked;

            // Unlocks the cursor position
            Cursor.lockState = CursorLockMode.Confined;
        }

        public void ShowMenu(string menuChoice)
        {
            if (!Enum.IsDefined(typeof(MenuType), menuChoice))
            {
                Debug.LogErrorFormat("Parse: Can't convert {0} to MenuType enum, check the spelling.", menuChoice);
                return;
            }

            GetManager<GUIManager>().ShowMenu((MenuType)Enum.Parse(typeof(MenuType), menuChoice));
        }

        public void RefreshHighscore(string difficultyChoice)
        {
            if (!Enum.IsDefined(typeof(DifficultyType), difficultyChoice))
            {
                Debug.LogErrorFormat("Parse: Can't convert {0} to DifficultyType enum, check the spelling.", difficultyChoice);
                return;
            }

            // change shown score data to the chosen difficulty
            GetManager<GUIManager>().RefreshHighscore((DifficultyType)Enum.Parse(typeof(DifficultyType), difficultyChoice));
        }
    }
}