The immediate response I get from customers when flicking between their previous setting and the calibrated one(s) are:
Colour - Lots more colours now apparent; subtle shade differences are now far easier to see, so the picture looks far richer and strong colours have far more punch without the whole picture looking over-saturated... this feeds in to the next thing which is detail. Although the sharpness control has normally been backed off, the work on optimising all the image processing and the extra colour contrast means that the picture now shows fine detail that was previously obscured. These both then feed in to the third most noticeable aspect which is image depth. Although most movies and TV being watched are 2D and the screens are essentially a flat surface, the work on the picture and the improvements they give make it possible to convey a greater sense of image depth where the original camera work has captured it.
Depending on the experience and dedication of the calibrator then calibration could mean anything from a quick tweak of the colours (greyscale) and setting contrast, brightness, colour/tint, sharpness through to a full-on optimisation of not only the TV but the entire display chain from source(s) to imaging device and everything in between. One approach gets a radically bigger improvement than the other. It's not all about money either, but it is true; you get what you pay for.
