The Facebook app has the same hamburger button and its design is very similar to OneDrive now, yet I didn't read so much rant about Facebook app design.
Again, it's not really about the hamburger button. It's about all the ways in which this app deviates from the metro design language. I think the hamburger button is the least important of those.
Given that W8 has provided us with a very recent example of how people react to jarring UI discrepancies, and that we know many people consider WP's design consistency one of its primary advantages, is it so hard to acknowledge, that this could be a serious issue, even if you personally don't think it's a big deal?
I think the majority of people react to design, consciously or unconsciously. I think deliberate design and conforming to guidelines is a very important component of what makes a UI easily learnable, particularly for non-geeks. I think it's one of the reasons WP does extremely well with first time smartphone owners, as you need only discover a few basic principles, after which you understand the entire UI. I think it's one of the things that helps the iPhone maintain it's perception of being high-end.
Keep this up, and before long, people will also start calling WP messy, just like Android (which is currently improving in leaps and bounds). I don't think that is hard to imagine. That doesn't mean I think metro is the be-all-end-all of UI design. I actually think it offers many opportunities for improvement. I just think such evolution should occur in a managed and consistent way, where all 1st party apps are used to set an example of what MS considers best practice.
Things like this obviously aren't the end of the world, but they do come at a cost. I don't think it's a good idea to ignore that.