It seems like an improvement. With Greenlight you paid $100 once and then either submit as much as possible until something gets notices, otherwise you wasted all that money; or your lone submission gets buried unless you do some do something to get people to vote, which often ends up being rather dodgy.
With direct you pay $100 (maybe - still to be decided) per submission, which gets moderated by Valve and (from the sound of it) your fee gets reimbursed if they like your game. All those bad games that are submitted pay for the moderation. If I understood correctly, once your first game is accepted you will be able to add more games directly without waiting for moderation, but you still pay a recoupable $100 per title. Presumably those get added to a queue where moderators can later approve your games, giving your money back, or even revoke your direct access if they think you're abusing the system (for example, acting as a proxy to let other devs skip the initial moderation to get bad games on the store).
That's all conjecture on my part based on few details that Valve gave away in their announcement.