All we've seen so far are the core mechanics.
Nobody plays D&D for the core mechanics.
People play D&D for the wealth of material -- adventures, monsters, magic items, adventures, spells, classes, adventures, settings, feats, and adventures.
We haven't really seen any of that stuff yet. I think they have a solid foundation upon which great material could be made. But will it? That's what matters. All those details matter. The sum total of those details matter. Not the core.
-- 77IM
(PS. Actually there is another reason people play D&D -- for the vast player network. I.e., people play D&D because everyone else plays D&D. That's extrinsic to the rules, though, so it can't possibly be judged in a play test.)