Blue Ray movie doesnt look like Blu Ray on ps3?

Im not sure if my question makes sense, but here's the deal.

I recently purchased a LG 47LK520 47 inch Class 1080p LCD HDTV along with a PS3. I have an HD box from comcast, and i also hooked up my PS3 to the tv with an HDMI cable. They work wonderful.

My only concern is when it comes playing Blu Ray movies. I heard PS3 is, if not, one the best Blu Ray players on the market. So yesterday i went out and bought Avatar in Blu Ray since i have once seen it at my brothers in law, and it looked AMAZING.

But when i try to watch it, it doesn't look like what i saw at bro in law. Not even close. I went online and tried to find on what settings i should have my ps3 on and what not, but its still not coming out to the quality i saw at my brothers in law. I have no idea what else to do. I already tried going out and getting another Blu Ray movie that i saw at a retail store being played, which also looked amazing, but it still didn't come out as good.