The main advantage of a plasma over an LCD is the contrast ratio (second is the non-ghosting refresh, third is the viewing angle). Watch an LCD in a dark room next to a plasma (which you'll never see on a showroom floor), and the difference becomes obvious.
I had a Sony Wega CRT and was planning to immediately upgrade to a Pioneer plasma. So I gave away my TV, bought a stand, and then got hit with some unexpected bills. So I couldn't get the TV I wanted. I figured I'd settle for a cheaper LCD. I hated every minute of watching that set. The old CRT had much deeper blacks. Luckily in the time I was saving up again, the prices of plasma fell by half, and their, already incredible, black levels improved further. So the set I ended up with is beyond my expectations.
The newest LED backlit LCDs can dim the light behind the screen in zones to match the expected levels on screen. Which boosts their rated contrast ratio in tests, but in real world viewing you end up with blocky areas surrounding each part of the picture of different level. Anytime you're trying to use a bright light to shine through a surface and then using that same surface to try to block the light you're not going to get the same deep blacks as when the surface itself is generating the light.
