Like most people, I have a lot of thoughts on this. They're mostly positive though. I think this was a pretty fun way to carry on the story and definitely am happy JKR said this is it for sequels. I loved being back with the characters again after all this time (always). I agree with some reviewers who said they didn't FEEL like these are the same characters we read about before. I think it more has to do with the format maybe? But definitely lacked some of the same snappiness they had before. That's really my only complaint. It kinda reads like really good fan fiction; this isn't a huge issue for me since its based on JKR's thoughts and "approved" by her as another installment. Still canon, in my mind. Not perfect but fun. Nothing about this "ruins" the original series for me - not one sentence. 
 Very general spoiler-ish things about the plot: I loved the time element because that's just a bookish favorite overall. I also loved the references to and actual scenes from years ago. Draco's involvement made me happy too! The ending made me tear up for sure. <3