I'd link
my reviews but you wouldn't understand much
I'd recommend being an asshole while writing reviews

A good critic needs to have a personality so that the readers can learn to know him. Strong opinions are good. Some will agree with you, some will disagree with you, everyone will get an image your film taste and it will be a more interesting read than a "safe" review. I don't use "IMO" or "my" in my reviews at all.
When you give enough content description (that's not plot referral) and the readers know you and your taste, they can interpret your review and see if it's a film they might like even if you hated it.
For structure, it's ideal if you can find certain topics that you want to explore in more detail. You don't have to mention every technical aspect of a film, that would easily turn your review into a list. For example, if you're reviewing a new Harry Potter film it's needless to write about cinematography and such things unless it's especially great or unexpectedly bad. It goes without saying that these big Hollywood are technically well made. Instead you could try to find some interesting point, let's say Potter and religion (ok, that sounds a bit boring but I haven't seen any of these film and don't know anything about them) that you explore.
Try to find continuety between paragraphs. Let the review find its form as you write it. Just go whatever direction feels natural. Don't decide how it's gonna end before you reach the final sentence.
Of course, these are just my personal views and not "facts".
I'm working on a review that is the most challenging I've ever written: Mamoru Oshii's Talking Head. The film is a sort of analysis of cinematic rules, with tons of dialogue concerning the subject. I'm writing the review from the same perspective, analyzing the film by using quotes from the film that the film itself makes about filmmaking. Creating continuety between paragraphs in this way is extremely challenging, not to mention the film itself is a extremely challenging. But it's a sort of experimental review and it's interesting to see if I can manage it. And I don't recommend this kind of reviewing unless you've written enough to get bored of "the same old structures".
http://www.imdb.com/title/tt0386065/