Shattered Crystal is not a good game even in the slightest.
It's a super generic 2D platformer that has basically nothing really tying it to the franchise even remotely outside of a handful of "race" levels where you spend 85% of your time watching cutscenes of Sonic racing around loops.
It suffers from the same problems Sonic Heroes did insofar as there's no reason ever to switch off of playing as Sonic until the game explicitly forces you to do so, usually just so you can hit a switch that's just slightly out of reach. Every single playable character is nearly identical save for a single special ability, and most of those special abilities aren't really useful outside of the exact explicit context they were created for. (Save for Sonic, who basically gets a double jump/air-dash that is more universally helpful)
It also twists your arm and demands you collect almost every single macguffin in the game before you can finish it. I think in order to unlock the final showdown with Lyric, you are literally, actually, seriously like 4 emblems/medals away from 100% completion.
If that wasn't bad enough, levels are intentionally set up to discourage backtracking. In order to collect enough stuff to get your medals, you usually have to play each level multiple times. All too frequently they will split in to an upper path and a lower path, and if you pick one, you have to replay the level in order to see the other.
All of the environments are uninspired and forgettable, the robot designs are uninspired and forgettable, and combat is brainless.
The best thing you can say about it is that it is not unplayable. It's not buggy, it's not broken... it's just soul-crushingly bland, like a ten year old licensed game based on the latest kids movie/tv show/whatever. You could probably do worse, but you should do way, way, way better.