If you have five spare minutes, Glass Cannon will fill them. Everything happens on one screen with 2 lives, bosses with 55 base HP every third wave, and the whole thing runs straight in the browser - no downloads, no sign-ups, no fuss.
Every third wave ends with a boss that soaks real damage and answers back. Regular enemies come in patterns - sine sweeps, dive bombs, wall formations - and each pattern has a spot where it cannot hurt you; finding those spots is the actual game.
Nothing here needs a tutorial or a wiki. Controls are one gesture, the goal is one sentence, and the difficulty comes from execution rather than homework. That is exactly what a browser game should be.
Endless waves, 2 lives, a boss every third wave.
There are 1 close relatives of Glass Cannon in the catalogue, which is unusual here. Comparing it with Hunt Elite takes about a minute and tells you more than any description.
Difficulty sits at Hard and the player count at 1. Those two numbers decide more about whether you will enjoy it than the theme does.
Keep it if you play in short bursts. It rewards a second attempt far more than a first, and the second attempt costs nothing but the tap.