Is there any term to describe stories where the "evil" characters are extremely evil, and the good characters are extremely good?
The answer depends on the work's intent. If the characters are thinly characterized and stereotyped because the work's main attraction is a sensationalist plot crammed with dramatic events, then we call this a melodrama. Wikipedia reports that a Professor Ben Singer has identified "moral polarization" as one of the key elements of melodrama.
On the other hand, if the characters are presented as contrasting moral opposites because they are intended to illustrate some larger philosophical idea, we call this an allegory. A famous example is John Bunyon's Pilgrim's Progress, where nearly every character personifies some virtue or sin.
EDIT: Based on your comments to your original post, I would note that Star Wars is basically a fairy tale, populated with archetypal characters. This style is sometimes called mythopoeic (sometimes rendered as "mythopoetic"). As far as Indiana Jones, I'm not sure it matches the request --the bad characters may be extremely villainous, but the good characters aren't exactly saintly...
A neutral term: black and white morality. Good and evil are unambiguously defined and, while a character can have faults, we never doubt its moral standing.
Typical example is The Lord of the Rings and Hobbit. The Silmarillion would be a bit of a stretch, especially when it comes to The Children of Húrin.
I don't know of a general, well-accepted term for such stories.
But I would say that "boring" and "simplistic" may or may not apply. There are many reasons why a story could be boring or simplistic other than having characters who are all good or all evil. And the converse is also true. A story whose emphasis is on plot development or the solving of a mystery may have simple characters because the author does not want to devote time to developing the characters, but rather to presenting and solving the mystery.
Also, you have to say which characters. Many stories have just one or two or three main characters who are complex and well-developed, and many peripheral characters who only appear briefly or sporadically in the story and so are not well developed. To take an extreme example, suppose in our story the hero has some valuable object, and for the story to work it is necessary for this object to be stolen and never be seen again. The thief may well just show up, hit the hero over the head, steal the object, and disappear. We would not be at all surprised if the thief is left as a simple, purely evil character, and his motivations and personal history are not explored at all.
"Extremely good" and "extremely evil" do not necessarily mean "simple". A character could be all good but still have a complex history and many conflicting motivations. Like, a good person could be torn between doing what is best for his children and doing what is best for society as a whole. Or, a story could discuss how this person came to be so good. How did he overcome temptations to do evil: to take revenge on people who wronged him, to cut corners on the road to success, etc.
In short: don't be simplistic in what you declare to be simplistic!
If you're referring to older, unsophisticated stories, where the author was being quite straightforward, then "clichéd" is probably what you want. (Plain old unsophisticated works too, or broad or simplistic.)
If you're referring to current stories, or your own, where you're aware of such stereotypes and you're parodying them, you might say you're being "ironic." That only works if you actually are being ironic and you're mocking the stereotypes by overplaying them rather than writing as though it's correct.