The original free version was probably the first horizontal shooter I put a significant amount of time into. Moving a ship and shooting things is such a fundamental video game thing but it took me until 2016 to appreciate the elegance of these games and the satisfaction (and addiction) that comes from repeating a level until you master it.
It loses some of its luster when you realize just how much it's influenced by Gradius/Lifeforce but is still a fantastic modern take on the genre. This version has some great quality of life updates and it definitely seems like one of the more forgiving examples of the genre. Still working my way up to the 100k achievement though!