I liked It!
Good story. Though somewhat simple, I enjoyed it a great deal. I'm grading the whole series here, so I apologize if I may come across as a little naggy.
I took off a point for the inconsistency of the voice work in the second. If it's in that one, I was sort of expecting it here.
I'm willing to look the other way for the sprite models since it is still absurdly difficult to find quality Blaze sprites in the Sonic 3 style.
The animation for part three definitely showed your improvement over time. It was smooth and clear, and I'm marveling at how you manipulated the backgrounds so they themselves had movement and seemed alive.
Initially I thought it was annoying how short the three parts were, Then I thought you probably had more important things to tend to besides the animation.
Your use of music was superb. You were able to find a wide array of music to fit the many situations throughout the series. The music didn't just fit, it fit WELL. Albeit the editing for the music could be improved a little, but not by much.
By the way. Would you mind if I asked where you got the song "Robotniks Lament" from? It was used in part 2 and just sent chills down my spine. It was so perfect for that "Ha ha, I have a weapon you won't fight" attitude Robotnik had.
And I have to give special acknowledgment to the credits for part three. The imagery of the Sol Emeralds floating down and restoring life to each zones, matched with the music, and matched with the different pages of the credits had a glorious sense of finality of the adventure. Yet it also left the door open for more stories and adventures in the future.
I hope that helped.