I love the jagged edge/pixelated cruelty of Vlambeer's games, and this is my pick for their finest work. It's extraordinarily difficult, insane, and an average game (or even a series of games) takes maybe 5-10 minutes. You no doubt know twin-stick shooting, and you know roguelike, but it's rare that a game has enough depth that I stick around for ~100 hours. That translates to something like 850 games of NT played. This goes onto my virtual shelf next to Binding of Isaac (though I think Isaac is easier).

Also if you catch it in early access, Vlambeer (flame bear!) continues with weekly-ish updates that add tons of stuff and tweak things. They are building the perfect shooter, and you deserve to play it.