Just picked up the PA 5500 because it was a great deal and I wanted an upgrade from a Panasonic 42" 720p (th42pxu I think) that I bought in 2006 for $700. The Panasonic is good but I've had the "purple crawlies" in greyish areas for years.
Have to say it's not much of an upgrade at all and in many respects is a step back. I set both tvs up side by side and had a monoprice hdmi switcher sending the same signal to each. Haven't done EyeOne calibration on the LG yet, but I did use the AVS test patterns to adjust brightness, contrast, and color. All "enhancements" are off, black level set to "low".
Viewing bluray content from only 6-7 feet away, I see no difference whatsoever in sharpness or detail despite the resolution difference. The blacks are slightly darker on the LG, but the brightness is significantly less -- on a 100% white screen, it's just quite a bit dimmer than on the Panasonic, even with Contrast maxed out (and power saving off) -- and this is even though my Panny is calibrated, so should be dimmer still. Pretty shocked at that and can't think of a reason why this should be. Side by side, the difference in size between the 42" and the 50" is insignificant as far as I'm concerned.
Another odd thing is that the picture and audio on the LG are slightly delayed compared to the Panasonic. I even switched the plugs on the switcher and the LG was still the one lagging.
Overscan is worse on the LG and I don't see anywhere to adjust it (edit: fixed it with Just Scan aspect). Curiously, the manual has literally no mention, much less explanation, of ANY of the menu settings, which are quite in depth (all greyscale and CMS options are right there, as opposed to having to go through a bunch of hiden service menus on the Panny). The only difference I can tell between ISF Expert picture modes and "Cinema" is the ISF modes split Sharpness into Horizontal and Vertical. Oddly, with all settings identical, the ISF mode is a bit brighter than the Cinema mode for some reason.
Glare is noticeably worse on the LG as well and this gives the picture overall a glossy feel while the Panny is more matte. I prefer the latter as it makes the picture seem sharper and crisper -- the "wet" glossy look kind of obscures details imo, as of course does the glare.
Sound is nothing great on either but the Panny's is okay while the LG's is really bad.
Honestly I expected a noticeable improvement from the 6-years newer tech, jump to 1080p, and increased size, but I just don't see it, and in fact in most respects, to my eyes the Panny is superior. Even at $350 it might not be worth it. Might end up returning this one. My only hesitation is the aforementioned purple banding on the Panny and some other issues I've been noticing lately.