I get the impression that you're shooting with a narrow-angle lens from far away. I think in some of these candid/people shots it would be better to shoot with a ~50mm lens and closer to the subject.
Great pictures, I like #2 the most, the shadows have add a lot to it....
btw where is this Gara de Nord?
I've been to two one in Brussels and the other in Paris yet it doesn't look familiar at all..