Very few of the characters are presented as either 'good' or 'bad'. Yes, a character may be on the
side of 'good' or 'bad', but few are wholly perfect or entirely evil. What I find interesting is that Tolkien is not didactic about how we 'read' a character; he presents us with what they do and how their behaviour impacts on other characters, but he does not
tell us what to think.
One of Tolkien's tricksy methods is to alter our perceptions of 'good' and 'bad' by having us view characters through the eyes of others within the book. Until the end of Book 3 we only see Saruman as others have seen him, so our opinions are already coloured by the opinions of characters such as Gandalf. Then we also get to hear the words of Orcs, and how they long to 'retire' from soldiering, how they view Men as 'filthy tarks'; hearing their point of view and paying attention to it skews our preconceptions.
Tolkien can also manage to make us feel sorry for some characters who we ought to feel pleased about getting hurt or being killed. The sad ending to Grima's life is just one case; brought low he finally 'snaps' but all for nothing. I know I also feel very sorry for the previously horrible Lobelia Sackville-Baggins at the end of the story. And then there is Gollum, who in the end turns out to be the one to 'save' Middle-earth, albeit inadvertently; I always think that his death is the only way he could have ended up, and that makes me sorry for him. With a character such as Gollum, Tolkien makes us think about 'good' and 'evil' and makes us see that we need to think about these concepts.
But as a mirror to this, his 'good' characters are usually flawed. Galadriel has a dark past, Frodo yields to temptation, Gandalf is sometimes impatient. In particular, Aragorn is a well crafted character in this respect. He is noble, but he can also sometimes be pompous in his words, and he even has something of the 'snob' about him as he almost refuses to give up his sword before entering Meduseld. If a 'good' character is
all good, then they would just be boring, learning little along the way, and possibly making us hate them for their perfectness.
Tolkien's not alone in doing this though, it's the mark of a good writer to make his or her characters believable. A lot of stories are even centred on how characters change and learn to deal with their flaws - Pride & Prejudice being a good case in point. I think where Evelyn Waugh differs is that he was a satirist, and such work often gets its humour and finds its purpose through exploiting stereotypes, so the characters often have to be more of a 'cardboard cut out'.