Have you looked at your Global Post Processing settings? Try and match those up to the free demos mentioned above. These can make a ton of difference to how a scene looks.
Also, how are you rendering your lighting? Have you manually adjusted your lightmass configuration? Are you building the lighting at the maximum (production) setting?
Have a read of:
http://bluevoidstudios.com/lighting-and-post-processing-study-of-ue4/
Also, consider putting in some spherical reflection captures on things that should be reflecting nicely.