Okay. The first thing I have to say is this: I can't believe this is a GBA game! It's a truly stunning piece of gaming mechanics that they got such a well-designed game onto such a titchy little cartridge.
The graphics, are truly excellent, considering that they are on an 18-bit machine. The world map in particular, is very well designed.
Sound is excellent as well, using headphones is the only way to go to really get a feel for the atmospheric music in the game. Sound effects are a little below par, but still very passable.
Gameplay is the most important aspect of any game, and on this particular one, it shines. It plays, I feel, rather like Final Fantasy VII in many respects. Whilst the storyline in this game is not on par with the one from FFVII (what is?), it's definitely a very sound story, which keeps you well rivetted throughout. The battle sequences are very well scripted. You need a fair amount of good tactics to get through many of them, especially a little further on in the game. In fact, I've not played a more difficult RPG than this. The difficulty is almost perfectly weighted.
In regards to the longevity of the game, I've played 25 hours, and counting already, and I don't think I'm more than half-way through. That's almost on par with Final Fantasy VII or X, which again, for a GBA game, is just phenomenal!
To summarise, therefore:
Golden Sun is:
A true RPG
Massive
Addictive
Portable!
Golden Sun is not:
Final Fantasy VII
For the faint-hearted
Good for your eyes, neck, or bum.
Graphics: 9 (It's on GBA, after all. Perfect for that, though)
Sound: 9 (music is perfect, sfx are not)
Gameplay: 10 (and probably 11, since it's portable. I'd play this game on a normal console, no doubt)
Longevity: 10 (Huge! It's exceptionally huge!)
Overall (Not an average): 10
Best game I've played on the GBA, without question.