I played around with the To-Do preview for a bit today and while it looks Wunderlist-like in some respects. For example, you can create multiple lists which can serve as context lists, project lists, etc.
On the other hand, the app seems to be more geared for those who want to create daily to-do lists. There's a default list labeled "To-Do" which seems to imply that that's where MS thinks you should put your action items. There's also a "My Day" list where you're supposed to put anything you should do today. Clicking an icon will generate automatic suggestions to add to the "My Day" list. So the thrust of the application seems to be somewhat antithetical to GTD.
Personally I steer away from solutions that try to guide you toward a particular workflow, especially if it contradicts the way I've come to understand GTD. But someone else may try out To-Do and think it's great for GTD and that I'm full of crap.
The other thing to consider is that for the longest time I've heard complaints about how there's no reliable, easy way to sync Outlook tasks to a smartphone. It sounds like To-Do will offer that functionality. That may be a boon for a lot of people.
FWIW,
@Louis, that's my take. But I'd urge you to try it for yourself. You're the only one who can determine if it will work for you.