It's the word "marketplace" that sounds off to my ear - too buzzwordy, and not descriptive of what's on offer. "Environment" might sound better?

The words "interactive" and "online" are fair descriptions of the service, but essentially made redundant by the phrase "directly in the browser".

Marketplace does suggest it's an opportunity for other people to sell their goods. Perhaps it hints at participation from outside experts not a part of Envy Labs that will become more apparent in later courses? The upcoming jQuery one seems to be run by an outsider.

Still, I think we're nitpicking on their copy here.

Out of curiosity, why doesn't everyone dislike 'marketplace'? A marketplace is where people sell things, CodeSchool sells things therefore it's a marketplace.

You're right. Look for it to be changed in the next round of design revisions.