Combined with burning the highlights it leaves the colours without much vibrancy because everything becomes more or less the same shade, and in turn makes the sig feel 'washed out' i.e. lacking any vivid colour or contrast.
Obviously I'm not saying that every sig has to be bright and full of colours, it's just that if you don't have some highlights and contrast then nothing will really stand out.
Screen is a bit unusual, going with low(ish) opacity Blur + Color Burn if the sig is too light or Blur + Soft Light/Hard Light if it's too dark are generally good options (Although, the blur is optional). The problem with Screen is that it brightens all the shades, whereas Overlay/Soft Light/Hard Light are more selective.
Other than that the composition on those recent sigs is pretty good, there's not much visible clutter and the flow is nice and clear. =)