Pokemon Sapphire is a good game, it will entertain you, I promise.
Here's a review:
Sound:10/10
The sound is great, and the music is awesome, so make sure you put it on full volume, you'll get a kick out of it.
Gameplay:10/10
The gameplay is perfect. Unless your game is cheap and screwed up, you will have no problems at all.
There are also mini-games like Pokemon contests and if you have a wireless adapter you could play with friends, like blending berries with them, battling with them, etc. Make sure you win for bragging rights. :-)
Graphics:100/100
I had to put 100 because the graphics are unexplainable. They are so nice, for a GBA game, the graphics are not even pixelated, they are just smooth. You will always recognize any Pokemon you see.
Adrenaline Rush: 10/10
I added this because this game gets you pumped up if you're trying to catch Rayquaza or Kyogre or Groudon. And once you catch them (if you plan to) that weight would be off you back, and you would be so happy because you accomplished something. Make sure you save after, I bet you wouldn't be happy if you game shut off.
So, if you have to pick between this game and another one, pick this one, it won't be a waste.