Aesthetic in the extreme, Enter the Gungeon is absolutely obsessed with guns. Many of the enemies are bullets, life is measured in crossed bullets in the shape of hearts, shell casings are used as currency, and every boss has a gun-related pun for a name.
The game follows the exploits of four gungeoneers come to claim the Gungeon's greatest treasure: a gun that can kill the past. It is with this gun that each of our intrepid heroes hopes to erase the greatest misfortune in their lives.
Generally seen as the yang to Nuclear Throne's yin, Gungeon's gameplay is slow and methodical like a proper bullet hell. Furthermore, where Nuclear Throne was centered more on interesting and diverse characters, Enter the Gungeon's primary concern is exotic weaponry, like a gun that shoots eggs that hatch into a cluster of bullets, or a mailbox that shoots letters (and letter bombs).
Though Enter the Gungeon is primarily a roguelike, certain measures are taken into the game design to replicate an arcade experience. For example, ammo is limited for all guns except for each character's starter weapon, and any dropped items left unclaimed will be stolen by the next time the player comes around.
At first this looks like a simple way to prevent power gaming and micro managing, but it also replicates the fleeting weapon and health pickups rooted in the genre's arcade origins.
In short, Enter the Gungeon is a love letter to twin-stick shooters, arcade roguelikes, and of course, guns.