When it comes down to it, evil is essentially selfishness, while good is selflessness. The majority of real people tend to be somewhere inbetween.
It's more than possible for a person to be likeable, nice to others and do good deeds, and yet still be evil, if the only reason they do those things is for personal gain.
The reverse can also be true - many an attrocity has been committed in the name of the 'greater good', by people who genuinely think they're doing what is best for others. The road to the hells can be paved with good intentions.
In Isle of Shrines I made the evil storyline all about greed, rather than child-eating psychopaths. The good storyline was about the quest for knowledge, rather than saving the world from 'bad guys'. The neutral storyline was about doing what was necessary just to survive.
I recently found a series of videos on Youtube of someone playing through the neutral storyline. It's weird watching someone else play your own module! However it's good to know that players are actually using some of the loot you designed (even bothering to read the item descriptions), and discovering the various secret locations and encounters you spend so much time creating.
Evil doesn't mean antagonist, and it is a wishy-washy concept. I did go "???" with Bishop just tagging every good guy as stupid. Okay, Casavir isn't really the brightest of the lot, and to be honest quite often I wanted to whack some sense into my party while playing the OC, but it just so appears that roleplaying game developers immediately tag some weird label of "stupid buffoon knight" onto at least one character... or maybe that's a trend Gaider started. Either way, they're about as flavourful as cottage cheese.
I didn't really find MoTB or OC campaign's bad ending to make much sense (most of the bad endings can only be explained away with the reason of "just because"). I guess this stems from my heavily story-focused style of playing. Reading through a few novels with "evil" characters being protagonists, I found that they all have much more interesting backgrounds than goody-two-shoes. I think Bishop would fit the bill in regards to this case, except his character was so badly written for me that I lost all interest.
Self-serving and evil alignment are extremely wishy-washy. Gann never seems to do anything for altruistic reasons, but he's neutral.
I think evil's got confused with bad/renegade and the whole alignment thing is flawed. I've never had any goody goody stuff in any of my modules and I've sanctioned the massacre of paladins, killing of unicorns and monks on drugs committing robberies. But it's all done for a good cause and a reason that is definitely not evil which is self serving, sadistic and quite frankly not nice in any shape or form.
Surely evil is the domain of serial killers, mass murderers, rapists and child molesters so it's rather nice to think that nobody wants to write that sort of thing and most people would rather play good/neutral characters.
Serial killers... is debatable. I'd qualify my Knight-Captain as a spree killer in some instances. She left a trail of dead behind her (she had good intentions and she saved Neverwinter, but I doubt the Watchmen she killed would appreciate it). She, for certain, is a "mass murderer". As for child molester, Casavir might well qualify for that category in quite a few playthroughs. And my Knight-Captain lies through her teeth. She wiggled out of almost everything by lying. She'd make an excellent politician...
Evil alignment is defined (very roughly) as "self-serving". Neutral evil, for example, is defined as pure pragmatism. But that does not mean sadism. Ammon Jerro's evil-aligned, but apart from killing his descendent (which he didn't know until it was too late), all he's done is pretty much save Neverwinter. Raistlin Majere is evil, but that's because he's put one purpose above all else (which would put Karsus in evil alignment too... maybe Dragonlance works differently). Artemis' code of conduct doesn't really fit the bill either (can't really recall him doing anything for his own pleasure... he was just really dedicated to his trade).
There's Cyric brand of evil (but he's crazy), and then there's Mask brand of evil. Most evil campaigns I see seem to want to make the PC into some weird devotee of Cyric type, but there are plenty of "evil" types that are intelligent, law-abiding, and self-serving.
I do see now, though, that writing a non-blah evil character is much harder than writing a good character. I don't think people wanting to play good characters being the issue here, since Raistlin is still the reigning king (queen?) of the series popularity contest... but writing a character as intricate as he is would be hard.
But I am getting a little tired - after 14, 15 years of PC RPGs - of playing "Batman". Having more Joker mods would be nice...