Wow, after the first two this one takes the cake as one of the best 2-D Sonic's ever, and among handheld games generally
Gameplay: 9
While the first felt like it was just Sonic 2 (which isn't neccesarily a bad thing, but still), the second tried to remedy it with the tricks and hidden little maneuvers. While that somewhat fixed it, it started to get old, and needed something new, and this game delivers. You start off just able to play as Sonic with Tails as your partner, but you can get more characters as you go. You've got the old jumps, spins, and of course running, but now your partner helps influence the way you play as well. First off, your jumping, jump height, and air-time will change depending on who's your partner, along with attacks and "tag action" which will be explained in a moment. If Sonic's your partner, you're gonna be jumping normally, but with Amy, your jumps are shorter and don't damage enemies.
Now, tag action is where you hold R until you're holding your partner, and then release, to do something different for each partner, on the ground and in the air. Tails will throw you up super high, Sonic will give you a HUGE speed boost, Knuckles will be sent flying into enemies, etc. In the air, it can change, sometimes alot, sometimes not, so experiment! The levels themselves are pretty well designed, although the large amount can get boring sometimes if you've played too many, but the Bosses make up for it.
Graphics: 10
The previous two had some nice graphics, but this game seriously pushes the GBA to it's limits, with sprite rotation, high-quality backgrounds and effects, and stuff on screen, you'll wonder if this is GBA or DS! Plus, as different partners change your actions, these different actions also have their own sprites, such as every character having a hammer when Amy is the partner. You really can't to wrong with these great graphics, especially some of the backgrounds, which you'll just love, from Sunset Hill's soothing background to Cyber Track's white-code like backgrounds, you'll fall in love with at least one level.
Sound: 10
Wow...just...just wow... everything is just great...
Every character has some actual vocal (however minor, it's tough to have that stuff in such a large game), and there are tons of sound effects, but sound can only go so far without music, which this game DELIVERS. Every level has it's own music, which is modified in different ways in between the three acts and the map, while the map is usually slow, the third act is usually fast, with the first being an in-between variation and the second being somewhat different from the rest. All this variation really does make a difference, and the game seriously works, you'll love the music so much, from Route 99's street-like effects to Twinkle Snow's upbeat winteryness, you'll absolutely relish it all. There are even five boss tracks, one for the bosses, and four for the last four bosses, PLUS the game has remixes of Emerl's theme from Sonic Battle along with the city theme AND a remix of the old Green Hill zone! This game once again shows that when it comes to Sonic, the game is ALWAYS going to please musically.
Story: 7
The game's weakest point is that it's story is very bland. Eggman has rebuilt Emerl from Sonic Battle as a black and gold robot to serve him. It's name is, strangely, G-mel, although G-merl would have made more sense. Still, it's not that bad, especially for a 2-D Sonic game, which are known to not focus on story that much. Still, at least something new would've been nice.
Bells and whistles: 9
You can play some single-cart minigames, OR 2-cart co-op! Yes, you heard me, co-op, and since it's being played on two GBAs, it's also a race! That, and the remixes, mini-games, bosses, levels, character selection, and chaos emeralds, all give the game such substance, with lots of stuff to do. You COULD get all the level's chao to get access to the level's secret keys to gain access to the level's ring collection minigame to gain access to that level's chaos emerald, or sit down and listen to music, or beat up Eggman, or play some multiplayer, or turn off the game and go to sleep (worst choice). Lot's of stuff to do, so much time. Ahhh.
Overall: 9
Easily one of the best Sonic games, and one of the best GBA games too, from vibrant colorful graphics to tight controls and awesome music, this game hits the higher points of Sonic games, failing only in it's almost complete lack of story.