I just finished playing through this. It's incredible.
Obviously if you've played a Bumper Engine game you'll have a reasonable idea of what to expect with the controls - not that that's a bad thing. It all handles VERY well. I always felt 100% in control and both the speed and sense of speed got to be really incredible at times. I saw some people criticizing the tutorial, but I actually really appreciated it. The tutorial gives you little slices of what to expect from the game and what to do - the bounce attack, for instance, being good for fast platforming. These are things that you see when people do their youtube playthroughs, but I always felt like they were just pros or speedrunners. After the tutorial it felt incredible to just blast through that first level, and feel like I knew what I was doing.
Which brings me to the second part that I really appreciated - something less common in 3d sonic fangames. The level design really blew me away. It's hard to understate how impressive this level design is. I'm not trying to put down other fangames either. Making a 3d sonic level is, with all its paths and speed and size is HARD. The levels in this game accomplish an important thing to me, which is being extremely complex but feeling simple. I never really thought about X path or Y path, or falling from one path to a worse path. I just felt like I was constantly moving forward. I was aware of paths that I was missing, but the transitions just felt so natural. I'm going to have to play this thing again a few more times to explore these levels because I'm having a hard time getting my head around the scope of those things. "4 levels" sounds small, but this is seriously like if you took sonic 3 levels and added a third dimension.
The bosses are fun, and still held up. I will say I didn't enjoy them quite as much as the main gameplay. The hilltop zone boss took me a really long time. Maybe I wasn't understanding how to fight it. Sometimes the homing attack would make me fall off the bridges. When that happened I'd spend a lot of time just catching up to the guy. The eggman boss felt like it had a lot of waiting between attacks, and more waiting between attack opportunities. I appreciated the floor slowly falling, which kept the fight fresh.
I loved the music and graphical style. It was a nice blend of genesis style (that jazz fusion ruled, especially in the pyramid level lmao) and SA/SA2. Big shoutout to the Eggman voice actor, he did a great impression. I'm not... super worried about the characterization of Sonic himself, but it did seem like he came off a little rude in the cutscenes? Like less confident, more arrogant. Also, I found that Tails' lines were always getting cut off. I'm not sure if there's an auto advance that was breaking or if it was my controller acting up. Maybe other people have had this problem idk.
I ran through a wall once in hilltop zone. Other than that, not a whole lot to say! It's great!