Has anybody played Kero Blaster? It came out in 2014 but I guess I overlooked it. It's on PC and Switch, probably other systems too. It's basically perfect.
It's made by person who made Cave Story, and there are plenty of stylistic similarities, but it's really a very different game.
It's 99% linear, more like a Mega Man (without stage select) than the Metroidesque Cave Story. It's short and sweet, I beat it in a single evening. It never felt like it was dragging on, and it didn't feel like it was over too soon.
There are points where it's difficult, but it never felt frustrating or unfair. To put it another way, it all felt very intuitive without feeling easy. The boss fights were easy to pick up on but still tense/challenging to finish.
Losing a life brings you back to the start of the screen you died in, so I never felt punished for little mistakes or individual deaths. Losing all your lives means you start the stage over, but you keep all your upgrades and money. What this usually meant for me was a chance to visit the store (one per level, I think) and upgrade something I felt was lacking.
The weapons are fun, too -- there's a basic blaster, a Wave (wide/spread type shots) a Bubble (shots roll downhill and float up in water), and a Fire (short range but intense flamethrower).
It's the most fun I've had with a 2D action/platformer type game in a long time, highly recommended.