The original plan of the game was going to have a story mode that played pretty much like a typical beat em up with a linear path (Kinda like the Scott pilgrim game). Metal Slug was also one of the inspirations and concepts that we want to make.
Unfortunately, because of time and effort for a fun little passion project, I had to cut it. I developed this game mostly for HTML5 so I can upload it on Newgrounds. HTML5 has a lot of problems so I had to make a lot of compromises mostly regarding the size and load times.
It looks like people really like this game so I'll reconsider adding something similar to that when I have more time.
Thanks for the reply!