I don't understand the amount of hate this article is getting from 4e fans. I don't see what's so offensive about it. It all sounds good to me.
The biggest problem Mike Mearls has at this point is that he's pretty much lost credibility with the two largest factions of the D&D fanbase. WotC completely burned all of its loyal 3.x fans with 4e. And since the announcement of next, there's been little said to 4e fans to make them think Next is going to be the experience they want.
So as of now, no matter what Mearls intends, the 3e crowd subconsciously adds "And I'm the guy who created 4e" to everything he says.
I take nothing that comes from official WotC channels at face value. Absolutely nothing. At this point, D&D Next could be anything from a literal reprint of 1e with ascending Armor Class and fewer saving throws, or it could resemble the most hardcore of hardcore narrativist systems with minimal dice rolling, and it wouldn't surprise me, because in my mind, there's nothing that makes me believe anything Mearls says in these articles has any real bearing on what the end product will look like.
For the 4e supporters, they're pretty much spot on (in my opinion) that D&D Next is very specifically a reactionary move against 4e. It's "D&D - The 'Oops, My Bad for 4e'" edition.
Mearls has never come out and said it, and never will. But the design elements presented in the playtest so far seem to indicate this is the case. I think most 4e supporters would be more apt to let it go if he would just admit it. "Yes, we're building this game as a reactionary move to re-position D&D with less 4e elements." I think most 4e fans would respect that level of transparency. Doesn't mean they'd like or buy the end product, but at least they could respect the man and the company that said it. At this point they're basically left to speculate while Mearls and other WotC mouthpieces dance around the issue.
So no, I'm not surprised at all at the criticism these articles receive.