GTA Advance is a very good, solid and long lasting title. It has great value and offers good mature entertainment.
First of all in GTA you've always had a free-style gameplay. Do what you want to do, and if you'll get bored - you have always the main missions. In those case, main character Mike has to complete 41 main missions on three islands. Cities are big and you'll have to drive for a while to get used and remember the most important places like: hospital, or police station. Missions are well designed, every next is a bit harder, so you won't be bored fast. Even after clearing main missions you'll have about 250 submissions to do for 100% game clearance. There is like always in GTA: vigilante, paramedic, firefighter and taxi missions. The best and easiest way to earn some money are taxi missions, but the other have some extras when completed.
Atmosphere of GTA is brilliant. Dialogs between Mike and gangs members are rough and doesn't sound to be read by a young player (as they never was). If you want - you can't have no mercy and go through missions like a Johny Rambo with tons of dead bodies - or like stealth and fast assassin: nice and clear :) In some cases you'll have to choose what to do in a current mission: fire this place up or make a small job and get the money back to boss.
Gameplay is more than good - cars behave and feel like in real GTA in 3D. Every car has own speed, acceleration and steering so you'll have to master every car to make a quick escape from the ambush.
Weapons? Huh, there is a huge arsenal: from baseball bat, through gun, shotgun, uzi, machine gun, bazooka, firethrower, grenades, and so forth.. You can even place a car bomb in your vehicle and blow some buildings up! (only in certain missions)
Graphics are just right for GBA. I think that it's even better than on PSX version. However, GTA Advance has some 3D environment like buildings, or fences, but it has an impact on the framerate. Sometimes it's just very, very slow. Music in game is awesome! Every vehicle has it's own radio, from techno in Diablo to hiphop in Yakuza - very enjoyable Soundtrack! Sfxs are great too - some speech like "I hope you have insurance" after collision with other car - makes a good atmosphere and feels like in 100% GTA :)
For me - this is one of the best mature and long lasting game. It has some minor flaws but it definitely take you straight to the raw, tough action from the first minute of gameplay!
Absolutely must have :)