It's worth mentioning that, since it's a beta, some of the instrumentations on these beta tracks probably wouldn't have been final. For example,
Angel Island 2 is missing a couple instrument parts from the final, is slower in tempo, uses different instrument patches, and so on. Carnival Night and Launch Base sound roughly complete here, but Ice Cap is obviously a bit lacking and probably would have received touchups before being shipped in the final.
That being said, I have to say I'm actually a little disappointed these didn't make it into the release. While the MJ versions generally work and do add a sense of atmosphere to the zones, it's very, very obvious that they were not composed in the same style as something like Angel Island or Hydrocity, and this is made more obvious by their lack of emphasis on melody and their uninspired Act 2 variants which simply mute channels from the first Act. I had always had some respect for the MIDI tracks because every composition gelled well with the rest of the soundtrack and felt distinct from the last, even if there were elements about the midi key or tempo which felt off; now that I understand their origin story, everything makes a little more sense, and I've a newfound appreciation for the Beta/MIDI compositions.
The biggest musical highlight for me is
Carnival Night 1. MJ's genesis tracks make Carnival Night appear a strange and unsettling, almost un-Sonic location. The Act 1 MIDI track makes it feel a bit chaotic and clunky. But the beta Genesis version perfectly encapsulates the zone as a quirky and lively theme park, which is just fast enough to match the pace of gameplay, while the instrumentation and chords really bring out the magic of the environment.