Reasons why you should get this instead of the HK dvds:

1. Good translation.  Agito is a series full of humor and mystery.  If you don't understand what's going on, you're missing 90% of the experience.  I heard the Hong Kong translations are terrible, incorrect names, bad grammer and spelling, etc.
2. Don't worry, these aren't the HK subs with minor English fixes.  These are translations straight from Japanese (I don't know Chinese anyway), so there's only one level of mistranslation instead of two.
3. High quality video.  I think I heard the Hong Kong dvds were encoded straight from the tv.  These are not, they are DVD rips, so the quality is excellent.
4. Good translation again.  OP songs are translated on odd number episodes, karaoke on even number episodes.  The battle song "Believe yourself" its translated in all episodes except the first
5. I do it for the fans, Hong Kong bootleggers do it for the profit (why else would they do such shabby jobs on their translation?)
6. Supporting me will help me to obtain new material to sub.  Supporting Hong Kong bootleggers just puts money in their pocket

Normal humans are helpless against them, bullets don't affect them, and they have unimaginable power, but there is hope.  3 Kamen (Masked) Riders appear and begin their battle to save humanity from this set of supernatural beasts.

Despite the grim description, KR Agito is a very, very funny series and a good drama.  The fight scenes are a must, but they are not what the series revolves around.  This is a series that puts all it's effort in excellent charaterization.  I dare people to watch this series and to try not like the main characters, it's just not possible.

Music:
The music for this series is pretty catchy.  My favorite is the main battle song "Believe Yourself".  The opening song "Kamen Rider Agito" and "Emergency Guard Chaser" are also pretty good.

Important People:
 

Tsugami Shouichi / Kamen Rider Agito: Shouichi is a generous, simple, all round nice guy.  His ideal life is to just work in his garden and please his foster family, the Misugi. However he is also has amnesia.  Plus he has another form that he knows nothing about.  That form is Agito.  All he knows is that he must become Agito to fight the Unknown, mysterious life form that kill humans What is Agito and why does he have this power?  Why does he have amnesia, what's hidden in his past?  And as Agito, how can he build his future?
Hikawa Makoto / G3 System: (Stands for Generation 3) The pretty boy of the series. Hikawa Makoto is a cop that wears the G3 System, a cybernetic armor designed to battle unknown life forms.  Hikawa is earnest, straight forward, and honorable, although also kinda simple and clumsy. His mission is to stop the Unknown from continuing their impossible murders.  He works in the G3 Unit with Ozawa and Omuro.  He spends a lot of time butting heads with his rival, Houjou Tooru. His comedy scenes with Shouichi (Agito) are the highlight of the episodes
Ashihara Ryou  / Kamen Rider Gills: Ryou's great, one of my favorite characters.  The bad boy of the series, he spends his time punching the main characters.  Still, you'll understand his angst when you see all the pain that he goes through. His journey to find acceptance with himself is but one of the many touching aspects of Agito.
Kazeya Mana: Mana live with Shouichi and her uncle Misugi.  Mana has some telepathic powers, but she keeps them secret.   How did she end up living with her uncle?  Why does she have these supernatural powers?
Sumiko Ozawa: The creator of the G3 System, she's one of the best characters in the series.  Raised in America, she's blunt and sharp tongued.  If anything is on her mind, she'll definitely let you know.  She oversees G3 battle operations from the G Trailer command base. Her fellow operator is Omuro, he's the comic relief, and does an excellent job at it.
Houjou Tooru: A fellow cop, he's like Hikawa's rival.  He's brilliant and talented as well as smug, evil, and sneaky, you'll love and hate him at the same time.  One of the most popular characters, there's just no one like him. He's also a character in KR Phis
Unknown: The mysterious enemy.  They possess powers unexplainable by science.  Why do they kill people and what are they after?

Bad:
This show is so good, but I know a lot of people will just never overcome their bias to try it...

Good:
Comedy, action, drama, excellent characters, deep story, this is my all time favorite Japanese show

Rant:
Masked Rider Agito is a tokusatsu or special effects show.  I know to most people, this may seem like a guy in a bug suit fighting rubber monsters or heroes in rainbow tights.  For the layman, don't worry, this show is about much much more than the fighting.  It has both amusing and despicable characters, all wrapped in their own dark past.

Agito has secret identities, people brought together by twists of fate, and a solid story filled with as many mysteries as there are characters.  It's kind of a children's show, but everyone can enjoy it.

Even though it sounds like a mostly guy thing, a lot of "young mothers" started watching it with their children.  The 3 main guys are extremely well developed, likable characters, but we all they were watching because they think the guys are cute, heh.

In short, Agito is a solid science fiction drama.  The main characters are both likable and believable in their roles.  Throughout the 51 episode series, the characters slowly unravel each other's secrets as they grow and change to challenge the mysterious monsters attacking humanity.  Even though the main story is a serious one about survival and evolution, the main characters are capable of great silliness during the many humorous scenes.

The battles are fairly choreographed and usually occur to the really cool song "Believe yourself".  Even if you don't like the fighting, the x-files like story and well written characters are strong enough to stand on its own.  In short, Agito is an excellent story for any sci-fi fan.

Engrlish:
This is on each DVD cover in English:
Wonder if the unknown force the mankind has gotten in hand is the forbidden zone of God, which should never be allowed to trespass?

"UNKNOWN", the scum being, slaughters over again as if it funks at God's punishment.  The three immaculate souls tremble, being tossed about by the destiny.

The distressing purity, the fathomless and touching delicacy and the worrying sincerity.

They still come not together in alliance.  They fight alone for the reasons of individuals.  All the intentions of the whole world which sparkle in the daybreak are downed in the deep oceanic blue and the people's mind undergoes continuing ordeals.

Bonus:
Volume 1 contains Vanny Knights 1 as a bonus episode

Volumes 1-9 contain the Interview and Battle scene music videos that were on the original Japanese DVD.  The interviews are subtitled, but the battle scenes aren't (it's the same as in the episodes anyway).  Some DVDs also have additional bonus footage like Sera Myu, HxH musical, bonus Kamen Rider clips, etc.

Kamen Rider Agito Hyper Battle Video and Kamen Rider Ryuki VS Agito Video are bonus footage on the dvds.  They are subbed off the original video.

Volumes 10-12 are 5 eps per disc, so I dropped the battle scene music videos for these 3 volumes.  You can get these music videos on a bonus dvd that I'll be creating later