I liked the Klingons, though I felt they were overexposed, particularly by the time of Enterprise. Similar to the Borg, I think the Trek writers kept going back to them because they were so recognizable figures and popular figures and didn't understand the concept of too much of a good thing.
Regarding the seeming contradiction of the TOS devious Klingons and the TNG honorable ones, I chalk it up to the vagaries of Klingon honor. It is supposed to be an alien culture after all and why should their concept of honor fit human notions? Also, the TNG era Klingons had some pretty devious characters too, like Gowron and the House of Duras, and the Klingon people or rulers seemed to have a jaundiced view regarding honor. Kmpec also was pretty much a pragmatist. The only one was steadfast about it was Worf, who largely lived away from the Empire, and perhaps had an idealized version of Klingon culture.
Regarding the seeming contradiction of the TOS devious Klingons and the TNG honorable ones, I chalk it up to the vagaries of Klingon honor. It is supposed to be an alien culture after all and why should their concept of honor fit human notions? Also, the TNG era Klingons had some pretty devious characters too, like Gowron and the House of Duras, and the Klingon people or rulers seemed to have a jaundiced view regarding honor. Kmpec also was pretty much a pragmatist. The only one was steadfast about it was Worf, who largely lived away from the Empire, and perhaps had an idealized version of Klingon culture.