As far as what to call 'downloadable games', I think that term suits it just fine.

The most useful use of the episodic treatment here is to give skeptical fans a taste of what the game's like. If they only spend $10 on a 4-level episode (made up numbers) and they hate it, that's more palatable than spending $30+ on a full game you hate and only play 4 levels of.

Sonic has not had the best reputation lately, though having the guys who made the GBA and DS Sonic games is a step in a decent direction. Though, I never cared for Sonic.