Strangely enough, I initially ignored the game due to this fact. (I downloaded it out of boredom to see if it held up to its name; which it did not.) I thought that it was some n00b who thought that they had a 1337xorz game that deserved the title Sonic 4. Personally, think it has potential, but I did not really like it due to a number of things:
1. Sonic just doesn't go fast enough. It is hard to go around loops, and the Spin Dash just doesn't work right.
2. The rocks in Act 1 look like foreground objects when they are in reality background objects. Then in Act 2, they are magically foreground objects.
3. The enemies were a little senseless. e.g. Compare your bees to the ones in, say, Sonic 2. The Sonic 2 ones are more so passive enemies than ones that hunt you down and gather over your head.
4. While the idea of combining Sonic 3&K and Chaotix bonus levels is interesting, the depth perception is a little wrong. It is too easy to misjudge a jump and fall off.
5. The level design is a little awkward. I can't put my finger on exactly what it is, but something is just not right.
6. Those rail cart things are hard to ride on. They tend to take off right before you land on them.
7. I am not sure of the reason that the levels are broken into parts, but I find it really annoying. Loading times = bad.
8. The fixed jump height. I think that has already been addressed.
9. There is a reason that Sega left out the detail of Sonic bouncing backward after hitting a wall in their games.
10. The game is glitchy overall. I have tried a few times to get through the surfing part, but there is a random glitch that causes me to crash at the ducking sections. Even though I am ducking, it still says that I hit the wall.
I hope that I am not coming across as unkind, but these are ways that I can think of that would better the game. Keep working on it, and maybe one day it will hold up to its name.