This pack is pretty ambitious. It aims to recreate Sonic The Hedgehog within Minecraft. I am absolutely impressed they even got it working at all but it does fall short in a few areas despite being really enjoyable for me. Sonic's gameplay just doesn't work well with blocks. I don't know how to describe it but Sonic feels like while going down slopes he stops and starts up again whenever he moves down a bit and it's just really janky and hard to deal with. This isn't much of an issue in levels like Chemical Plant and Sky Sanctuary but in Green Hill it's reaaally annoying sometimes. It has a bunch of bonus things though like an unlockable mode in Tails' computer, super Sonic, achievements, Chao for the Chao garden as a reward for completing achievements, Amy and Shadow, and probably more I missed. It's also packed full of references in Tails' workshop. This pack was enjoyable enough despite it's short comings and I don't regret playing it.
Just a tip make sure to map running to an easy to reach button and turn off "FOV can be altered by gameplay" it makes it way better.