I thought it made a pretty decent final boss for the demo, all things considered. I mean, Sonic 2's final boss was basically the same thing in a smaller arena, even though there was another fight with Silver Sonic before that. There've been worse final bosses in Sonic. CD's, for example. Or any of the Game Gear ones.
Sonic Triple Trouble's final bosses were awesome. I only remember a few of them though. Sonic Chaos, on the other hand, had a pretty lame finale, as did Sonic Blast. Also, the true boss for 3d blast was lame compared to Panic Puppet.