Exception

Taken in the broader context of the Edo period, the Akō Incident is an anomaly, representing possibly the only case of a lord being avenged by his retainers. Of the 118 separate revenge killings recorded during this time, 115 were carried out by family members avenging a slain father, brother, mother, or uncle. Two of the three remaining incidents were perpetrated by non-samurai, leaving the Akō vendetta as a unique case of retainers carrying out a revenge killing during the Edo period.

Inventing the Way of the Samurai: Nationalism, Internationalism, and Bushidō in Modern Japan.

One's lord, at least in theory, was of course very important to a samurai. However, how that theory translates to reality differs from person to person. There were people who committed seppuku to follow their lord in death (it stopped, or at least was minimized, in the Edo because it was outlawed), and there were people who would betray their master for personal(or clan) gains. On the whole I would move to say that, as a group, samurai in the sengoku were a bunch of disloyal thugs.

/u/ParallelPain has linked you the book on the development of the concept of Bushido, which mostly happened after the samurai period and well into the 20th century. That may be disappointing to hear, but it doesn't mean that samurai didn't have their own codes and ideas of how to behave, just that there wasn't one all-encompassing code of "Bushido", which was the same in every place for centuries. I've found the varieties of ideals, and the behaviour that actually happened because of or despite of the ideals really fascinating. If you get into Japanese history, there are plenty of amazing stories.

One of the most accessible explanations of the history of Bushido as a concept comes from a historian interacting with interested inquirers on the internet: Karl Friday's posts that comprise The Historical Foundations of Bushido. I think this is exactly where you should start out reading.

http://www.koryu.com/library/kfriday2.html

Friday's notes point to further reading on the subject. He finishes

Two places to start, though, are: G. Cameron Hurst, III, "Death, Loyalty and the Bushido Ideal," in Philosophy East and West 40.4 (1990); and my article, "Bushido or Bull? A Medieval Historian's Perspective on the Pacific War & the Japanese Military Tradition," in The History Teacher 27.3 (1994)

You can find both those articles online, and they both examine the story of the 47 Ronin:

Hurst: http://enlight.lib.ntu.edu.tw/FULLTEXT/JR-PHIL/ew26464.htm

Friday: http://ejmas.com/jalt/jaltart_friday_0301.htm

Now, if you want more stories of revenge, as /u/ParallelPain explained, the 47 Ronin are unique in avenging a lord, but avenging a family member, for instance, was sometimes mandated. There's an article on the subject which you can read for free on JStor:

Kataki-Uchi: The Practice of Blood-Revenge in Pre-Modern Japan D. E. Mills Modern Asian Studies Vol. 10, No. 4 (1976), pp. 525-542

http://www.jstor.org/stable/311761

But if you want a fun discussion of this article and revenge in samurai Japan, I highly recommend this episode of the Samurai Archives Podcast: EP30 A License to Kill: Blood Revenge During the Edo Period

http://samuraipodcast.com/webpage/ep30-a-license-to-kill-blood-revenge-during-the-edo-period