It's recommended that you keep your blog postings to a maximum of 500 words. In fact, most places who will feature you as a "guest blogger" have this as a requirement! The idea is that people lose interest fast when viewing web pages and especially when reading something online. If you find that you're not keeping readers for anything other than giveaways, this may be your problem.
I will even admit it--if I see a blog post that's really long, I will either skip the entire thing or just skim for details. Now a blog post with more photos, less words, and just main points--I'm hooked! To combat this problem, I often divide up posts with long content. Making a "Part 1" and "Part 2" can actually bring traffic back to you since more people are willing to read the shorter blog post, get interested, and then decide to come back to find out more.
As far as reviews go, stick to your review! Don't regurgitate the details of the product that someone can read on the retailer's website. They're reading your post because they want to know your opinion of what you liked and didn't like. Give them just the basics about the product, or you're going to risk writing that super long post again! Many times, authors of blog posts feel that the more details, the better. While that is the general rule for much academic writing, the same rule does not apply in the blog realm. Stick to the basics, write shorter posts (or continuing shorter posts!), and leave questions to the reader. You'll find that more people will take the time to read, and more people will leave comments relative to your post!