The screen on GBA is indeed very dark. This is because it is not backlit, and is designed to work with direct lighting. Very frustrating - my son has one and I gave up with trying to see what was going on!
Experiment with shining different lighting angles, too. Lastly, there is a little bright LED "lampost" available for the GBA which plugs in the back (still allows piggy-back machines to connect), but this does drain the battery.
[ 08 October 2001: Message edited by: sanjosebaz ]