I've had a Samsung 50" plasma for 3yrs and I still love it.
The sharpness the OP saw at Costco could be due to the TV setup. Retailers will set the TVs they want to move into flame mode (high contrast and brightness), ie makes the picture pop to draw attention.
A good test is to run a low quality signal to the TV and see how you like that picture. Death by TV info can be found at
Display Devices