It's a rogue like zelda 1 like dungeon crawler.
You have 1 life to get through a 20 - 45 minute long game. No saving. The levels are randomly generated along with the loot, upgrades, bosses and secrets you can find. There's quite a plethora of items, multiple characters to unlock and play, along with deeper and more difficult floors depending on how many times you beat the game.
I've thrown in 30 hours into a game I bought for 5 bucks in the humble bundle.
It also has really good music.
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Brawl is like ZSS' breasts. Well rounded for casual players
http://img.imgcake.com/YetAnotherShadow/Gameboyfeverjpegez.jpg