I do agree that it's "just the way it goes-" people vary in their tastes, and in their priorities in looking at what constitutes a "good book." For some people, typos can break a book, others are looking at characters, still others look for plot or theme, and some look at writing style. I know sometimes I read a book, write my review, then look at other reviews and think "wow, did we read the same book??" Apparently, my priorities and how I judge the book weren't the same as some other readers.
I looked at your reviews on Amazon and on Smashwords, and it's very interesting that the vast majority of your reviews on both sites are from readers who have *only* reviewed your book and are vague about what they liked, exactly. As a reader, that doesn't give me the information I want to be able to make a selection, or give you helpful feedback. (One 5-star reviewer on Smashwords reviewed it halfway through and gave it 5 stars, then gave it another 5 star review when he finished? That was, err, unusual...)
Overall, if you're looking to improve based on your reviews, I'd say that there was some talk of a simplistic writing style, and praise for the actual content and plot. So if you think the comments made are all honest and you want to take the suggestions, then maybe beef up the details and the level of language (a few commented it seemed more like a YA book) in your book, but keep the same great ideas. That's my read
Whatever you decide to do, best of luck! Writing a book is hard work, and sometimes the feedback can be difficult to swallow.