In case (hopefully) this thread gets lots of replies, I'll keep a list of which anime and manga have been reviewed, with links to the posts. And feel free to do a series that has already been reviewed, everyone has a different take on what they've seen.
Naruto - 
If you do decide to submit a review, while you don't have to write a 5 page dissertation (it would actually be better not to), you should try to add some detail and support your opinions. Here's an example of a good review and of a bad review.
Here's a review of the anime series "Naruto" by Kishimoto Masashi.
Naruto is a shonen anime about a young ninja boy named, you guessed it, Naruto. Naruto's dream is to one day become Hokage, the leader of his ninja village. However, the road to becoming Hokage is long, and there are many challenges he must face before he can claim his title.
The cast in Naruto are both varied and numerous, with characters to appeal to a very broad audience. One nice thing about this series is that many of the characters actually have some depth, and develop as the series progresses. You can actually watch them grow, rather that watch a static crew go through different situations. Unfortunately there are points where characters will suddenly seem to revert to their immature behavior just as a plot device. Despite this, the way the characters are handled is a welcome change from most shonen anime, where for the most part the only thing that changes about the main characters is how powerful they are.
Voice acting is a little sub par, at least in the dub. Most of the characters either seem to be almost completely emotionless, or are more overexcited than a caffeine-influenced 5 year-old. And then there's Naruto himself, who almost every other line shouts out his catch phrase "Believe it!" which really starts to grind on one's nerves after the first million times. Luckily, most of these problems can be easily remedied by watching a subtitled version. The Japanese voice actors seem to have put more care into it than their English counterparts, and if you don't understand Japanese, then hearing "Dattebayo!" every few lines is far less irritating than hearing "Believe it!" (if you do understand Japanese then you're outta luck there. Sorry).
Where Naruto really shines is in the plot. Engrossing story arcs keep you on your toes until the end, and then leave you eagerly anticipating the next installment. And aside from some weak filler episodes later in the series, the pacing is handled quite well. You don't have any parts over before you can even grasp what's going on, but you also don't have to deal with fourty episode long arcs which seem like they will never end (I'm lookin' at you, Bleach).
In the end, with interesting and innovative ninja techniques, an involving story, and a wide range of likable albeit occasionally cliched characters, Naruto is a great example of the shonen anime archetype, and is worth a look for anyone into the genre.
That was just an example, there's no need to conform to that length or format. Anyways, here's an example of what you'd want to avoid.
I love naruto it is so AWESOME and sasuke is so kawaiiiiii GO WATCH NOW!!!~!~!
Yeah.... Don't do that. Not just here. Don't ever do that. Anywhere. Ever. Seriously.
Anyways, I hope that this thread gets lots of posts and you all benefit from it. Happy reviewing!