I got a GameBoy Advance SP yesterday and as you might have notice I refrained from posting about it that evening. Which in turn kind of explains how happy I am with the little gizmo.
The box it came in is very small, but an even smaller space within it is reserved for the actual unit... Actually the box is only there to house the adapter. The best thing about it are probably the micro-switched buttons and d-pad (anybody who had the joy of using the NeoGeo Pocket's d-stick will know what I mean).
About the screen; it IS darker than the screen of the original GBA. This is probably done to counter the wash-out effect the frontlight produces when it's turned on. Also the L- and R-buttons are smaller but that doesn't make them uncomfortable. On the contrary, you can now use the middle portion of your finger to press them and it feels strangly 'relaxed' (as opposed to the 'tentacle-grip' I needed for those buttons on the GBA).
So overall very good! As for the headphone-jack. Who cares! The internal speaker is louder anyway.