Sonic is a fun game that is good for long car/airplane trips.
Gameplay:
Pros - Controls are clear and reasonable. Enemies, powerups and traps are very easy to identify on screen.
Cons - Buttons are a little small on a GBA. The controls take a while to get used to.
Graphics:
Pros - Runs very smoothly, even on a GBA. The little animations are nicely done. The scenery clearly shows the boundaries of where Sonic can go, unlike some other games where the ground is a thin line.
Cons - No 3D, not even imitation 3D.
Sound:
The sound is only music with power-up picking and stuff like that. The sound comes out of a tiny speaker so the quality is horrible.
Value:
If you're going on a long-distance trip soon, this game is pretty good for the road/plane.