I believe this is the greatest game of all time unquestionably, the replay value is simply fantastic.
If you buy sonic and knuckles this game improves even more as you can open the cartridge and stick sonic 2 inside this cartridge.
I first played the game way back in 1992 and it is such a good game I played it as recently as yesterday and tend to play a few times a week it is simply brilliant. There are cheats availible to enhance gameplay and the game ending changes depending on how many emeralds are collected through out the game. If all seven emeralds are collected sonic turns into super sonic but it is a real challenge getting all seven emeralds so you will need to try a few times to get all seven emeralds and replay value is high as you can keep playing until you complete game with super sonic.
The game is relatively short but can be played over and over again there are 10 zones 7 have two parts one has 3 parts the other zones both only have one part so this mounts to 19 levels plus the final boss level which takes well over 5 minutes.
There are 20 well designed levels totalled and there are seven special stages all of which are top class and you aim to get an emerald in each one, if you playing with sonic or sonic and his companion tails you can become super by collecting all emeralds.