I caught an Enterprise rerun (couldn't be bothered to catch very many episodes of it when it was running) that explained it. According to that series, Klingons always looked like TNG Klingons. However, the K military or whatever performed an experiment in genetic engineering using some of the data that created the group of engineered humans (Khan and cronies) that resulted in a deadly virus that dissolved the cranial ridges, etc and made the infected Klingons look like TOS Klingons. The doctor saved the day figuring out how to prevent the virus from being deadly, but only after millions had been infected and turned into TOS Klingons -- with the genes that would turn their children thus as well. Kind of nice that they fixed that little mystery.

Now, while TNG was a very nice re-envisioning of the Star Trek universe, there are only a few gems of episodes and a whole lot of -- again, stilted acting and rehashed stories. Watching the reruns on Spike TV is highly repetitious, most every episode is just a slight modification on the one before, it seems. Now, DS9 was the superior show (imo) towards the end. There was actual, in depth character development, and story lines that extended over a whole season and even across seasons. It was darker than the others, but I think it managed to improve the franchise. That is, ignoring the last couple of TNG movies that were rather disappointing (did we really need The Wrath of Khan remade with Picard? I don't think so.)

- JP