If anything in a store looks head and shoulders better than something else, there are a few reasons, one of which is that they set them up to look that way. Best Buy was just nailed for doing exactly this, very recently. An LCD display can't do black as well as a plasma. Period. LCD displays are, however, really good in a bright environment. Still, bad video distribution, improper setup and wanting to sell Samsung LCD TVs over Panasonic or Pioneer is based on profit or inventory levels. Sometimes, they get kickbacks, which are used to effectively lower their cost.
The KURO plasma does black better than any other display than any other that I have seen. Dark gray is not black and if realism is desired, good black is an absolute necessity.
Blocky picture and digital artifacts are from weak signal strength, not the inherent ability of the display. If it's rated as HD, blocky doesn't enter the equation. Grab the remote and go into the menu, so you can find out if the brightness, color levels/tint/hue, contrast and sharpness are whacked. Look on the back to see which inputs are being used but don't be surprised if they aren't using the HDMI or component inputs.
If you buy the Panasonic, Pioneer or Samsung, you will need to calibrate it, but you will have a really good or great picture.