The backlight on LCDs ages and eventually burn out if it's florescent. If it's LED-backlit (newer technology) that's not a problem.
LCD's don't give you true blacks only dark grey although it's getting better. Plasmas have true black.
Plasmas are best watched in dark rooms because glare is an issue for glossy screens.
LCD's are generally less expensive, but good plasmas are now quite reasonably priced.
Thanks for this info.