It looks like an old Flash-game and to a certain extent it plays like one too. Just move around dodging enemies and projectiles, while picking up gems to level up. And that's just about all there is to it. Vampire Survivors is incredibly simple. But like the best clicker and idle games, the devil's in the upgrades.

With every level up, you can add a weapon or skill, or improve one already in use. There's a careful balance here. Every single upgrade often doesn't do much. Unless you pay attention and plan ahead. Which is made more difficult by the (semi-)random nature of when which upgrades appear. Stack accordingly and half-way through a time-limited run, a single upgrade can break the dam and you can turn your character from a fragile little sprite into a frame rate crushing projectile death-machine.

That in itself would already be just fine, but the game wants to maximize those positive vibes and does so by way of treasure chests. Left behind by boss enemies, picking these up will start a slot-machine like cycle as you get a random upgrade for free. Extra lucky? Then the chest will provide you with three, and sometimes even five - FIVE - free upgrades! The audiovisual cues that accompany these moments of random joy are deeply intoxicating and you may find yourself bopping along to them in a seemingly ritualistic fashion as you prepare to slaughter the undead hordes with your increased powers. And after Death inevitably claims your mortal coil, and your heart rate subsides, you are left with gold to buy permanent upgrades and give it another shot. Because, who knows? Could even Death be killed with enough upgrades? Only one way to find out…

Is it good then? Absolutely. A dangerous template for purveyors of loot boxes to ensnare their audiences even more? Very likely. One of the best time-wasters this side of de-Flashed Newgrounds.com?
My friend, why are you dodging the opportunity to find out for yourself?