I never have any issues with the screen brightness inside. I find that the GS3's auto brightness is calibrated to exactly how I like it.
The screen is definitely harder to see outside in bright sunshine. I find this to be the case for most phones anyway. Personally, I don't use my phone often when outside. If I do, it is harder to see the screen, but not impossible. I use my phone in the car for navigation almost all the time. If the sun shines on the screen, it makes it harder to see, but I can still see it. If you are using your phone outside often, it just takes a little while for your eyes to adjust.
This is my exact feeling as well on all counts.