Ah goodie, a HT question...
Its not just the image quality, but often the ability to adjust said image that makes tv's expensive.
Calibration of tvs for proper image projection (which extends the life of the tv, btw) is essential in myopinion, but requires adjustments to the greyscale, in addition to the basic brightness and contrast settings. Most peoples perceptions of a poor image tend to come from an 'incorrect' image being displayed. When you go into a store and see a good or bad looking picture, what you're actually determining is what image looks closest to what your brain thinks is correct, and spotting the 'quality' of a screen by looking at it is in fact very difficult to do.
Unfortunately, the majority of lower priced tvs do not have the controls to enable you to tune to a correct image, and most tvs in general do not allow for the primary colours to be adjusted.
In general, look for 1080p, a good refresh rate (over 120) and wide viewing angle. If you are playing games through your tv from an xbox, ps3, etc then refresh rate is vitally important.
Now a note on playing media from another device through your tv...
- 1080p is definitely what you want right now, but make sure your other devices (bluray player, etc) support it or you wont be getting the full benefit.
- Other things like frame-rate, pull-down etc make a
big difference to how your blu-rays and DVD's appear and perform through your tv
- Firmware updates on your products IS important
- Some brands of hi-fi gear have better decoders which work better with other models. This is worth considering aswell.
- One brand of player doesnt necessarily work best with the same brand of tv!
There is SO much more I could say, but a lot of it is tech-talk that most people dont care about. Good Luck!