This, combined with Sonic & Knuckles, is the best classic Sonic game of all time.
*NOTE: This review explains both Sonic 3 and S&K combined.
The story takes place immediately following the events of Sonic 2. Sonic and Tails investigate a floating island where the Death Egg has crash landed on. Upon reaching the island the guardian of the island Knuckles the Echidna takes away their chaos emeralds, under the assumption that they are there to steal the island's precious power source, the Master Emerald. Throughout the game Knuckles continues to try and stop Sonic and Tails. Despite that Sonic and Tails still go in search of Robotnik and try to stop him once more. This was the first game in the series to feature a more story-driven plot and it serves the game very well.
Gameplay is set up like the previous titles. You still run and jump very quickly through various stages. Each zone contains two acts, with a sub-boss at the end of the first act and then a fight with Robotnik at the end of the second act. The acts this time around are bigger, more fleshed out, and offer more chances of exploration. All of the game's levels are pretty much connected together, giving the effect of going through one huge world. With the complete game you will get the biggest Sonic game in the Genesis library. There a few new additions to the gameplay. In the menu you can choose between Sonic, Tails, and Knuckles. With Tails you can fly around for a short period and swim underwater. As Knuckles you can glide, climb up walls, and destroy certain obstacles that Sonic and Tails couldn't. In the game you can also collect elemental shields. The fire shield protects you from fire and gives you a mid-air dash attack, the lightning shield absorbs any nearby rings, and the water shield protects from drowning and gives you a bounce attack. Another innovative feature to the series is the inclusion of a save option, which makes continues you may earn practically worthless.
Returning from previous titles are the special stages. This time around you will have to find giant rings in well hidden areas to access them. The special stages are set up as a sort of overhead perspective where you need to guide your character to a set number of blue spheres. You will need to clear the blue spheres in specific patterns, otherwise you may end up running into a red sphere which ends the special stage. As you continue through a special stage you will progressively run faster which makes things more tense. These stages are certainly rather challenging, but some memorization will make them a little easier. You will need to collect all of the emeralds to fully complete the game, but it doesn't stop there. With the addition of Sonic & Knuckles come Super Emeralds, which you can only collect after collecting the corresponding chaos emeralds before reaching the Sonic & Knuckles story arc. Completing the special stages for the Super Emeralds will unlock a special super form for not only Sonic, but Tails and Knuckles as well.
Graphically there is a much greater attention on environmental detail and the character models look a lot smoother. The game is also still incredibly vibrant and colorful and the environments are very well designed. The music is also fantastic. This marked the beginning of Jun Senoue's legacy as probably the finest composer of Sonic series (and the soundtrack even got some help from Michael Jackson, though he was uncredited). The music in the game is simply fantastic and it's just as memorable and catchy as the previous games.
To sum things up:
PROS:
-Superb graphics and music
-Well designed environments
-A good amount of large levels
-Super Emeralds are a good new addition
-Fantastic gameplay overall
-The addition of a save option
-Good story for a simple 2-D game
CONS:
With so many great additions to the already fantastic gameplay, and the overall size and scope of the game, this is certainly my favorite of the 2-D Sonic games. This is an absolute must own for all Sonic fans and fans of platformers. This is an absolute masterpiece of a platformer that you really shouldn't miss out on.