This engine is a good example on what's possible with blitz sonic, it does have little flaws, but most of the small things that I didn't like are because I'm used to the other Blitz Sonic engines. Nibroc did a epic job on the models, didn't think that we would see so many old characters playable in a game again.
The new graphical effects surprised me, didn't think that something like this would be added, very nice(it limits custom characters by a bit, but sonic world wasn't made for custom stuff anyways), the only thing that I didn't like about the new graphical improvements is the blurr/special effect in the skybox, there is no way to turn it off but that's probably a bug.
The character moves are good for the most part, I liked the new added moves, some moves(omega hover) could be a bit better and I'm hoping that Fang and Bean get new extra moves soon(I already got ideas for that).
Some of the stages/missions won't work with some characters but that happens because the stages were built for Blitz Sonic Heroes, where you always had a fly/power/speed character, this isn't a big problem because this game will get more stages in future updates, which are made for every character. Not sure why you removed Love Garden, it was one of the stages that worked well for almost any character if not all.
The stage missions could need a bit more help, thought that I had to explore the stages and collect some things to get a good highscore for the time mission, but it looks like you have to get to the goal as fast as possible and speedrun the game to get a good rank on that, while you have to explore on normal missions, a bit strange and I think a different ranking system where you can get a good rank by speedrunning or exploring.
The missions are ok and work well, exept for some small things(red ring and gold enemy/all enemy missions might have little problems on some stage), the only mission that I didn't like is the ring mission, get hit once and you are back at 0% complete or even need to completely redo it, it can be very easy to get hit in this engine, so maybe the mission should be changed so that the ring counter goes down but not back up.
If you haven't played Sonic World yet, go play it NOW, it's a great 3d sonic game.