Sonic Adventure had fair difficulty for its time. People were still figuring out how to both create and play 3D games properly, so by today's standards it is a breeze to play.
The real crime is that it's almost 2016 and there still isn't a Chao Garden app on my phone. Fallout Shelter is the closest thing, but it's not the same. 
I don't think Sega is ready to bring the Chao back just yet.
