This is one of my favorite Sonic games. The OST is easily my favorite in the series, which is saying a lot. This game also has my favorite story of any Sonic game. I love travelling around the world and seeing all the cool locations based on real world locations. The day time levels are a blast to play through and are easily the best parts of the game. The night time levels are also pretty fun, but they can go on for a bit too long sometimes.
The single worst part of this game is medal collecting, it is just such a hassle to have your progress halted because you need to find some medals in the levels. The final boss also is not great.