Borderlands is a game with a huge, massive story with 4 characters efficient in different weapons. There are literally MILLIONS OF WEAPONS
No 2 weapons are the same! You could have 2 of the same gun, with different stats! EX: You could have 2 of the same revolver, but the other would have a extra dmg bonus or regenerating ammo. With great DLC like The Zombie Island of Dr.Ned (Who is totally not Dr.Zed), you get to fight zombies, undead birds, zombies that throw barrels at you or have loot chests on there back, or you can fight CL4P-TP, Also known as Claptrap in Claptraps new roboloution!

The binding of isaac is heavily based off the book of the same name. You are a crying baby whose mother tried to sacrifice him for god. As the game progresses you get new items. You start as a baby, who turns into a demon thing or something as you get more items that edit your visual appearance. You can unlock other characters with different stats. Each dungeon is randomly generated, so infinite replay value. The game has a perma death, so that means you gotta start over if you die. You can also kill the 7 deadly sins, and the 4 horsemen of the apocalpyse after killing mom to the first time. the second time you get to go to a new chapter: THE WOMB, and fight her heart. Everytime you defeat her heart, you get a new item except up to 10 times, you get a new character that time. after 6 times the games harder. after 9 times, the heart is replaced by IT LIVES, a tougher living version of her heart. You can also unlock new variations of bosses. Even the bosses are randomly generated! -FIN

Sandbox? Physics? Addons? optional content that require other games? Ill take it!