As an author, I let the reviewer say whatever they like, but there are some reviews which I don't find helpful when I'm deciding which books to buy.
1. Reviews which could apply to anything - for instance, "I loved reading this. I couldn't put it down. The author has done a great job, and I want to read more of her books. I'm giving this five stars!" Yes, but what is the book about?
2. Reviews which make it clear the reviewer is unfamiliar with the genre. If someone says Love of a Highlander is the only romance novel ever to have a Scottish hero, there may be other things wrong or inaccurate about their review.
3. Reviews which are poorly spelled, ungrammatical and so on. I once read a review which referred to a character's "unborn adolescent".
I don't mind spoilers in the review, but there should be a warning about this at the start. And I always like to read a reviewer's opinion as well as what the book is about - a good review, IMO, shouldn't just be a rephrasing of the blurb on the back cover. You could say how this book compares to others that the author has released, what it contributes to its field, what didn't work for you, etc.
I personally vote that you write BOTH. Not an author here, just a blogger, but an aspiring writer. I have had some interactions with authors who appreciate personal feedback. Just mu opinion.
I'll check out your blog! Here's mine:
I tend to start out my reviews with a brief summary of what the book is about, while avoiding major spoilers. I try to make sure that this covers aspects such as the setting and the main character.
After that, I tend to give my own opinions/commentary/criticism of the book. One thing I value in a review is objective honesty. I don't enjoy every book that I read, but if I don't like a book, I explain why. Different people like different books for different reasons, so someone else might love a book that I disliked.
Some bloggers like to use a system of stars for their books. I don't, because I find giving a book a star-based rank to be rather arbitrary. The reasoning for whether a book is enjoyable or not is more important.
I think that the biggest way to get more comments is to network and visit and comment on other people's blogs. It helps to find people who have similar taste in books as you do. Also, if you're posting at all on this site, I'd suggest linking to your blog at the end of a comment, as it's easier for people to find you that way.
Best of luck!