So I'm not sure what there is to get upset about. I don't see any big functional changes in the OS aside from reworking the notification center UI a little- and I like this new version more. It's already been confirmed that they aren't locking down apps to the app store or anything like that.
It seems like people think that because they're taking design cues from iOS they intend to lock it down like iOS and they're transferring that fear into dislike of the new UI itself.
Apple knows that a large percentage of the people who buy its computers are software engineers and if they ever do fully lock their computers down in that way they'd be ceding that marketshare entirely, along with catching quite a bit of heat for it in the press. Maybe eventually that calculus is worth it to them but I don't think that's what this is a step towards. I think they just want users who are fully plugged into their ecosystem to feel like it's a cohesive experience across platforms and this achieves that.