The matte screen has a definite and perfectly-judged sheen to it and is beautiful to look at, as well as being better to work with if you do any kind of image editing/retouching.
Choosing the gloss screen seems to me as daft as taking out some clear boot polish and shining it up on the screen. It's a fad that might make shoot-em-up games look more "dynamic" by over-emphasising the reds of all the blood splatters and exploding heads, but that's about it.
I'd say the 17" LED matte high res screen is a very significant and highly worthwhile improvement over both the standard 17" screen and the 15" LED screens.
But if you go the gloss route, you might as well just stick with the standard screen.