You can go to the SAMSUNG site and compare them side by side.
As you move from the 450 series to the 950 series the contrast ratio's get bigger and the resonse times get shorter. Plus starting with the 6xx series it has 120 mhz motion flow.

What the site will not tell you is this. Starting with the 650 the screens are glossy making the picture better but reflecting light. However the 630 which they just came out with has a matte screen like the 450 and 550 series making it a better choice for bright rooms.