Our jury came down on the G25 for oversaturated colors and overly dark blacks--while the blacks were indeed very deep, they seemed a little bit too deep, as though the TV was "rounding down" the shades of dark gray into black. The net effect was that the colors were certainly vivid, but the oversaturation made everyone in our test clips look a bit sun-burnt, and the too-dark blacks meant we lost a lot of detail in dimly-lit scenes.
The GT25 has taken a reasonable step towards fixing these issues. They're still a bit oversaturated and too-dark, but less so than the G25. When we compared the two side-by-side, the difference was clear: the GT25 doesn't look fantastic, but it does look significantly better than the G25, and scored slightly better than the G25 TVs across the board. Ultimately, the GT25 landed a 3.3 overall image quality score over the G25's 3.0 (out of 5)--not bad, considering most TVs typically score no higher than 4.0 in most respects.
The 3D features were roughly comparable to the other 3D sets we've seen on the market, like the --and considering the price difference between the two, that's a good thing. When we tested the 3D features with Ice Age 3 on a PlayStation 3, they looked appropriately deep, and a few effects (like snow splashing on the "camera" lens) looked really good. Of course, they're not going to look as good as they do in the theaters--no current TV does--but it's not bad at all.
The GT25 uses active-shutter glasses which are notorious for creating blurry, flickering images, but the Panasonic design team did a good job minimizing their effect--the flickering wasn't terribly noticeable in our testing room (even with the lights on, surprisingly) and I didn't notice any outstanding problems with the 3D image quality. The included glasses are still rather heavy, however, and when I wore them on top of my corrective lenses my nose got tired after about 15 minutes.
Don't expect too much from the built-in 2D-to-3D upconversion features. It's a neat toy to play around with every now and then in case you find something that works better than expected, but for the most part it's rather unimpressive (though it makes the built-in menus look great).