Thanks for the feedback! Development hasn't been abandoned, it just takes a long time to work out sprites and backgrounds all by myself, it's still actively being developed behind the scenes almost daily, there's new levels and control reworks being made as well to fix some outstanding pain points I noticed new players have with the Metal Slug control scheme, mainly aiming down as well as running forward while aiming backwards (think Metal Slug 3 first boss). That may involve changing the control scheme altogether, which is a tall ask for MS fans, but may be a necessity for introducing new players.
About the projectile speed/visibility and overall pace, I'll keep that in mind for sure, it may come with the next resprite and new level update that may come along some time in the future.