If you have five spare minutes, Rookie Wings will fill them. Everything happens on one screen with 5 lives, bosses with 45 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.
It suits anyone with a queue to wait in or a kettle to watch: students between classes, commuters, parents stealing ten quiet minutes. There is no meta-progression to lose and nothing to catch up on - a week away costs you nothing but a little sharpness.
Endless waves, 5 lives, a boss every third wave.
There are 2 close relatives of Rookie Wings in the catalogue, which is unusual here. Comparing it with Iron Ship takes about a minute and tells you more than any description.
Difficulty sits at Easy and the player count at 1. Those two numbers decide more about whether you will enjoy it than the theme does.
The practical advice: play it once with the sound off and once with it on. On this board the difference changes how you time your moves.