Sonic 1 and 2 had been excellent games, despite a few issues such as occasional pacing problems. All too often a third entry is adequate, but not up to the standard of it's predeccesors. Here, however, is where the Sonic series perfected it's craft. It is likely that the series will never reach so high a tier as this again.
Note that I am reviewing the locked on version, as it is how the game was originally planned before time constraints necessitated using the lock on function.
I will begin with the game play. The player now has the choice of Sonic, Tails and Knuckles. Sonic plays as we have always known him, apart from a new "insta shield" move and new elemental shields that give Sonic new abilities.
Tails now has control over his iconic flying move, which was surprisingly unusable when playing as Tails in Sonic 2.
Knuckles is the new character, and his gliding and climbing abilities change the game play considerably. Knuckles's levels are also designed differently, differentiating Knuckles's campaign from Sonic's and creating replay value.
The level design is sublime, finally perfecting the balance between large amounts of speed, excellent platforming and exploration. In particular, the exploration in the game has increased from the previous entries, and there are several routes through levels, along with hidden areas to explore, usually leading to special stages. The reason the level design here has so much more of an impact than previous installments is that the three elements I mentioned earlier, Speed, exploration, and platforming are now in correct balance, whereas I thought that the previous games occasioanlly failed to balance these. The levels are much more expansive and can be awe inspiring.
There are 13 zones, not including the True final boss. These are varied and make good use of level tropes that the series had not used by this point, such as wintery areas and deserts, and most zones have their own small gimmick allowing things to feel fresh.
The bosses are also much more inventive and there are also now minibosses in Act 1 of each zone. These feel unique and fresh compared to the rather standard bosses of the previous games.
The graphics are vibrant and glossy, and show flair and style. The music is classic and memorable, containing emotion and atmosphere.
An excellent game overall.