My favorite in the series
The main reason as to why I love it moreso than the others is due to the fact that it has the most levels (which all vary in themes well), the ability to play as any character (along with a separate story for knuckles' game) and the inclusion of super and hyper transformations.
It's definitely the easiest game amongst them, but that doesn't stop it being highly enjoyable and challenging occasionally.
Most people agree on Sonic CD to be the best game; however I find this game much more varied and memorable in terms of music/levels/boss battles/transformations and so on; to me it just gives you more value for money.
Just a few points on my views on this fantastic sonic the hedgehog game, which is what it's all about.