By perspective I mean the way you made the background. If you look at a sidescroller like, let's say, the first Mario Bros. In that game background is flat, it has no depth. Your game has depth, like in Captain Commando, for example. It has a vanishing point.
You don't have to play them, just take a quick look at videos in case you need inspiration for visuals/interactions with the background.
Also check how the characters move. No need to add that type of movement to your game, I just wanted to offer you some insight regarding what has been done.