The Star Fleet Universe did a way better job with the Klingons than normal Trek ever did. They go into way more detail about their society and flesh them out a lot.
They have the reputation of being fearsome warriors, but that is because that's the image their military has worked very hard to promote in their dealings with other races. The average Klingon civilian is not that much different from a human being, albeit with a significantly lower standard of living in most places. This is due to the Klingon Empire being poorer than the Federation, and having an overinflated military budget. In fact, their fear of being economically dominated by the Federation is the main cause of their antagonistic relationship with them.
Also, in the SFU, the Klingon Empire is an actual empire, encompassing many different subject races. The Klingons themselves rule over all of them with an iron fist. But on most Klingon ships the crews are primarily made up of these subject races(although never in a command position).
Paranoia is fairly common in Klingon society. Their subject races are not happy, but they rarely, if ever, try to revolt. The few that have were made dramatic examples of by the Klingons. Because of the tense situation within the Klingon state, they have the ESS, or "Empire Security Service". The ESS is basically a secret police organization that watches everyone like a hawk. They have broad powers and report only to the highest levels of the Klingon government. Their agents are everywhere, and even Klingon starship captains fear them.
Within the Klingon military, there is a very strong code of personal honor, which is very important to them, but they aren't buffoons like modern Trek Klingons. They don't fight to the death mindlessly while screaming about glory. To them, there is more honor in living to fight again and succeeding than sacrificing their lives needlessly. In fact, such an act would be considered laughable and idiotic by SFU Klingons. But they also would not hesitate to sacrifice themselves defending their homes and their empire if the situation required it.
Man, if only they had kept going with the Klingons as they had been set up in TOS. Then they could have been actually interesting, instead of a bunch of flamboyant and predictable cartoon characters.
