Mos Speedrun is like a coin pusher at the arcade. You keep telling yourself that you can beat it in just one more try. Because of this the player gains far more satisfaction from succeeding, especially after their fifteenth death this level.
So, let's talk plot: you appear to play an orange ladybug-thing and must run to a postbox as fast as possible. You must avoid bees and what seem to be zombies with football shirts on. Since there doesn't seem to be any actual plot, I like to interpret the story thusly: the world cup has turned every football fan into zombies, and insects have grown to human size. You are a brilliant scientist ladybug-thing and must post the cure in order to distribute it.
That's not a terrible interpretation of the plot, shut up!
But seriously the game is simple arcade-gaming fun. The controls are as good as they could be on a flat screen with no physical buttons, the game is easy on most levels, but only if you take your time and don't go for any goals.
In order to unlock new sets of levels you must get a number of points, you get a point for each goal on each level. These are completing the level, getting all the coins, finding a hidden skull (hey, it's more original than stars), and what I consider the most difficult point to get: speed challenge.
In order to get this you must beat a level in less than a set time, which usually required the optimum path with max speed and no mistakes.
The graphics are low, but the game cannot be criticized for this as it is intentional, for a retro aesthetic.
The music is catchy and very nice, fitting well with the fast paced game.
To sum up, Mos Speedrun can be frustrating at times, but you will ultimately come back and win it. The developer has perfected the "easy to learn, difficult to master" method that is common in arcade style games (or is at least attempted in most arcade games).