Too tiny, too busy by far.
As the title says, your game window is much too small for the extremely busy level of graphics in each level. Because the game doesn't support a proper method of scaling into fullscreen, I have a hard time picking out individual objects and comprehending anything that's going on on-screen. The character is difficult to find and harder still to re-find when he goes through doors.
In short, you shouldn't make the assumption that all your players are going to be running an absurdly low screen resolution that will enable them to see what's going on. Use a larger window next time or support scaling. Or better yet, do both.