Doing a very quick test on my GS70 (Japanese, not that it should make a difference), feeding it footage from Sony Vegas:

The best viewing angle is when the LCD is angled slightly downwards. This will let you see into "superwhites" and "superblacks" (colors above and below legal white and black level). The GS70 doesn't record superblacks, although it does record superwhites (like the majority of cameras).

If you angle the LCD upwards, you can see superblacks but not superwhites.

If you view the LCD head on, you can see neither.

2- How to tell the LCD angle:
Look at the top of the LCD screen. You should not see a sliver. You should see a good deal of the top face of the LCD screen.

3- How to test: Use a program that can generate superblacks and superwhites.
In Vegas, Anything over 235 235 235 RGB is a superwhite value when using the sony Vegas codec (NOT the microsoft codec).
anything below 16 16 16 RGB is a superblack value.
Use the SMPTE Bars. Use the solid color generate to superimpose squares or polygons over the SMPTE bars where the 100% white bar is, in the lower left. Use the pan/crop/masking tool to cut out polygons.

FCP can generate superwhites... stick the birghtness and contrast filter on and crank brightness.

Ok looks like I shouldn't make broad sweeping generalizations. :D

If you put real world images on the LCD, the image doesn't look right if you angle the LCD downwards. You do however get to see into superwhite detail. It's not very accurate for seeing superblack detail, although it is possible.

It seems like the best thing to do is to look at the LCD straight on, and angled downwards. When angled downwards, look at highlights for highlight detail (which you can't necessarily see straight on).