While you're not supposed to obsess over bad reviews, sometimes thats a little hard to avoid. The part that stung the most was that my amateurish work was full of spelling and grammar mistakes.
One problem is that, at least in the US, you submit your work to the KDP and then release to the world. Center/centre, color/colour and a number of other spelling differences are simply going to be wrong. The real buggers to find are homonymic misspellings. One that I caught after the initial release and corrected was heal/heel ("He turned on his heal"?). I'm sure there are others. This is one place where Kindle publishing shines because it is easy to upload fixes. Finding these homonymic errors is one place where the new Word shines, it underlines them with a blue squiggly and it convinced my linux-loving husband to let me get a windows machine.
Grammar is different. In one simplification, there are two parts of novel, dialog and the rest. The rest should be in reasonably clean English. However no one really speaks in perfectly grammatical English. If you think you do, listen to yourself. You'll be shocked at what you hear. So my dialog attempts to be realistic, which means "nuts to you" if you're a grammar nazi. That said I do have a tendency to write long and complicated sentences, and a history of proof reading my husband's scientific papers has inured me to the passive voice.