Hey Ad,
First off that's a cool looking structure. I did agree with Jeffrey's thoughts that the sky was too bright as that was my first thought. Your title is gloomy, which to me means that sky should be darker.
From your edits, I like the original structure the best. In #2 where you darkened the sky it looked better. I think I would darken the sky even more. Once the sky is dark enough, then I would play with how bright or dark the building is.