I know that this pack was originally made for 2.1, but I'll step in anyway.
I think that the level design is great, with pleasant visuals, good texturing, fun to play through, and just overall interesting as a whole. However, it has some questionable design choices due to the original being from 2.1, such as the overuse of certain enemies that were made more powerful on 2.2.
Another pretty bad design choice is the way you find Radiant Caverns. How are you supposed to know that you just have to fall down a random pit in a random stage, and bam, you suddenly get transported to a new stage? As neat as that stage is, I just think that's straight up bad design. There are a few other smaller things I could comment on, such as the lack of slopes (especially in the first level).
Along with that, I personally don't like the inclusion of Score Emblems. They were probably removed from 2.2 for a reason, as getting them often requires you to explore every inch and cranny of the stage, and if you make a mistake, you might not have enough rings to get the required score. It's especially bad in Chemical Facility, with both acts being too big as a whole, leaving little room for error, or requiring the use of an overpowered character (like Sonic Overdrive).
Either way, I still think that this is a pretty good pack, and despite shortcomings in a few certain areas, I would recommend giving it a go. Just don't try to 100% it, as some levels are painful.