It was definitely still D&D, and I've been playing D&D since 1st ed (~ 1983).
To me, what makes a game "D&D" is what you do, not how you do it. For example, the preview adventures were the same sort of things you'd do in 3rd ed, 2nd ed, 1st ed. No change there. The 'how' was obviously different, and that's the whole point of having a new rules edition.
I had a LOT more fun than I might have had in 3rd ed. The reason for this is the surgical removal of a lot of meaningless minutiae that tend to drag down a game's pace. A minutiaectomy, if you will. We were able to move things along very quickly, so much so that in one of our "delves", we got through 3 encounters in 30 minutes! Try doing that in 3rd ed.