This is a nice, completely free-to-play 2D retro style single player platformer along the lines of VVVVVV with a lot of exploration and traversal. One might call it MetroidVania style since its a big open world that has you moving from screen to screen. Each 'room' is only a screen like the original Zelda. Since you are exploring, there is no map. The controls are simple, left and right to move and a jump button. On certain platforms you can hit down on them to fall through the platform like many old school 2D platformers.
Where's the challenge? When you get hit by an enemy or spike you die instantly. Luckily there are checkpoint bells everywhere on almost every screen. When you die, you instantly respawn with no load times. It really keeps you in the action. It is very similar to VVVVVV but much easier and relaxing. If you get frustrated easily, this might not be the game for you, but since you respawn, there's no real punishment for failing.
The game takes an hour or so to complete. For the most part the game is easy fun. It starts out calming and relaxing as you explore, but eventually has tricky platforming areas and intense bullet dodging boss battles. Along the way you'll find loot bags. What do they do? Nothing but an achievement at the end if you collect 100% of them.
Progressing through the game, you will enable different things such as solid blue blocks, solid purple blocks, double jump and so on. To enable each thing, you must get past the boss. I say get past, because you are just a boy in this game with no combat. You will dodge enemies and in the case of a boss, dodge dozens of bullets on screen at once. The bosses fire in patterns, so you will get the hang of it. There is not that much enemy variety, bats, snakes and crabs move left and right, spiders move up and down. The game's main enemy is spikes.
Since this is a retro style game, by default the game has a 1980s monitor feel. Thankfully you can turn off the 1980s monitor and see everything full screen with no added glare. For anyone that finds the game too easy, there is a remixed level design which is much more difficult yet still forgiving with checkpoints everywhere. If you are brave enough there is cat mode that features 9 lives and YOLO that has one life and then its game over.
This is an easy recommendation, but if it was $1 or more challenging I'd be hesitant to recommend, but this feels like a good game for the developer to make a better game with. Solid controls, the understanding of an easy beginning headed toward difficult end.