There are 5 difficulty settings in Metro Exodus:

Reader

This difficulty is best for focusing on the reader/exploration aspects of the game. 

What it features:

• Enemies are easy to defeat and resources and ammo are plentiful.

Choose this difficulty if 

• You want to experience the story and/or don’t enjoy fighting enemies.

Easy

This difficulty is best if you want to play the game as standard but a little easier or less stressful if you're not the best at Fps shooters. 

What it features:

• A little harder than Reader but resources and health packs are still easy to come by.

Choose this difficulty if 

• If you aren’t that good at FPS games but still want a bit of a challenge.

Normal

This difficulty is the standard choice to experience the game for most players. 

What it features:

• Standard Difficulty, enemies are a challenge but not overpowered.
• You will have to watch your ammo count and approach every fight with caution.

Choose this difficulty if 

• You want to play the normal difficulty setting for regular FPS Players.

Hardcore

This difficulty is best for those who find standard difficulty a little too easy. 

What It features:

• Enemies are more dangerous as they have higher health and do more damage.
• Ammo and Resources are scarce.

Choose this difficulty if 

• If you want a challenge, best for shooter veterans.

Ranger Hardcore

This difficulty is for those who want a real challenge. 

What it features:

• Removes reticule and hides most of the HUD.
• Enemies are a lot more aware and skilled, you need to pay attention to your surroundings. 
• Ammo is very limited, weapons degrade much faster, and crafting benches where you can repair them are rarer and further apart in the game level.

Choose this difficulty if 

• You want to experience the ultimate challenge in Metro.

My Personal Opinion:

The best difficulty for me is Normal as I like to experience games at the setting that keeps everything balanced, not a piece of cake nor a frustrating try-hard overpowered enemies filled shoot fest. At Normal difficulty, just enough skill is required to progress through the game and time can be spent on engaging deep into the rich lore and story without too many distractions or frustrations.

Also Be Sure To Read:

• [Top 5] Metro Exodus Best Armor (Body and Helmet) (And How To Get Them)
• [Top 10] Metro Exodus Best Weapons (And How To Get Them)
• [Top 5] Metro Exodus Best Electronics/Bracer Upgrades (And How To Get Them)
• Metro Exodus Best Difficulty - Which To Choose
• [Top 10] Metro Exodus Best Settings For Great Gameplay