A great Gamecube game and what I personally think might be one of Sega's best... it got an official PC release too. This platformer has charming visuals, a lovely soundtrack, a really unique gameplay type, and elements that cater a bit to both score attack and "collect-a-thon" fans while staying its own. It's even got some of that 2000s-era Sega/Sonic Team togetherness, with cameos from Sonic, Nights, and even Phantasy Star Online.
An absolute time capsule of Sega's legacy + a genuinely fun experience all the way through. Yet it seemingly hasn't been re-released anywhere since the PC port was made in 2006!