You have a great piece here and I think it’s just lacking a little drama. That drama needs a story or a FOCAL point. That can be done with a little light. Right now your piece has one overall value or tone and the viewer just needs to know where to look. That window gives a perfect opportunity to impart some light into the scene. I hope this gives you some ideas on how adding values, darks and lights to your art can improve the overall appearance and feeling.