Vampire Survivors is a top-down survival game where you essentially just try to stay alive as long as possible while endless waves of monsters come at you from all sides.
Your weapons and abilities are all automatic; you just need to worry about moving around the map and staying alive. Some of your abilities only fire in the direction you're facing, while others target the nearest enemy, and still others just randomly fire off and hit anything in their path.
Extra strong enemies will drop treasure chests when they die, which will give you gold and a random ability to enhance your character.
As you gain XP and level up from killing monsters, you'll get an option to pick your next ability. Choose wisely; you're given three random abilities and you can only choose one. Make sure you pick something that will help you survive long enough to level up again.
You fight until you're eventually overwhelmed. Then you pick a new character (or the same character if you like) and start over again. The more gold you earn, the more core stats you can boost from the main menu, which will give you a starting advantage in your next playthrough.
There's a timer on the top of the screen that shows how long you're surviving. If you start to do really well, you'll unlock more levels to play. And honestly... that's pretty much it. It's just a fun game to see how long you can overcome insane odds against hordes of monsters. Pretty simple, yet rather addicting. A great way to pass the time.
I loved vampire survivors, I have not played it in quite a while. I did just pick up halls of torment and that's scratching a similar itch.