I salute Spyro 2 for being ambitious for the GBA from 2002, but unfortunately the system isn't well designed for a game of this genre.
For ease of comparison I would say that Spyro 2 is in the same genre as Mario 64 or Banjo-Kazooie. You must collect fireflies that open additional worlds in the game, just like Mario's Stars or Banjo's Jiggies. There are also a couple thousand gems to collect that I guess are kind of like Banjo's notes, but they serve little purpose apart from completion's sake. This is as far as the comparison goes, because whereas those other games are great, Spyro is not.
The isometric view in Spyro makes for awkward gameplay. I can't remember a game where I've walked or run off a platform so many times. You'll get walking under control, but still, press R for charge at the wrong time and you're dead. Any time you have to jump over a pit it's like a roll of the dice whether you'll make it. These issues do get somewhat better with practice, but the learning curve is disturbing considering my familiarity with the genre, and I still found myself tiptoeing around to avoid falling off.
The gameplay is pretty dull, too. You've got just a few moves at your disposal, and aside from the constant danger of a misstep the game is rarely actually difficult. There's a decent variety in level themes but each world is over and done with too quickly for them to leave much of an impact. A few kangaroo and shooter levels do little to break up the monotony of walking around, shooting puffs of fire or ice while hoping not to fall to your death at any time.
I've played worse and I guess for the GBA or DS you're not going to find much better in this genre. It's too bad that GBA can't be played on the 3DS because the joystick might help. As it stands, this game is difficult to recommend even to fans of the 3D collect 'em adventure genre. You'd be better off pulling out your favorite game of this type and giving it another go. You'll be glad you did.