There has been a fashion recently for games to offer moral choices, well in reality they have done this sort of thing for years but only recently has the trend become fashionably such that they make a big deal about it. I quite like being given the option and will often play the evil path because I am a sadistic bastard. Then I'll play the good path for completeness after that following the evil path again just to make sure I have extracted as much negative karma as possible in a process I like to call sucking the marrow from the bones.
Bioware have done this sort of thing for quite a while even back to the Black Isle days with the classics like baldurs gate and Planescape Torment. More recently they have tried to bring this in to the next generation of action rpg's like Knights of the old republic, Jade Empire, and of course Mass Effect. While I still think their grip on the action side of the action RPG is more tenuous than it should be they are very good at the story telling part if you like that sort of thing. However they still fall foul of making their paths somewhat simplistic. Various others have tried this Bioshock, Fahrenheit/Indigo Prophesy, Fable, Black and White, the Deus Ex games, the Fallout series, Oblivion, Morrowind, and even the new GTA all to some degree had components of choice to them but some were better than others.
Partly the point being able to choose is that choice has some sort of consequence and for some games the promise more than they can deliver. For instance the much hyped moral choice in Bioshock visceral and emotionally loaded though it was (the first time at least) had little or no impact on how the game played out. It didn't influence the story line except to give a different ending in fact in some ways it made the story fall to bits if you played the evil path.
It's also the case that the evil path is somewhat simplistic veering between moustache twirling villain stereo type or as Byrnie phrases it puppy kicking. Then again the good paths are not much better usually being so sickeningly good as to stretch credibility beyond anything like reality. Mass Effect tried to side step this by having the Paragon and Renegade path but it really didn't make that much of a difference it was still basically good and evil path except it was a bit more random occasionally you could do the good/bad thing by mistake. I suppose this lack of grey in these games makes them less believable the true evil path is unlikely to be so obvious the kind of casual violence that they use as a substitute for any more subtle way of characterising an evil path makes things a bit pantomime at times.
I don't mind linear stories in games, some of the best stories in games have been linear, but if I'm promised some sort of storyline that includes choice I'd prefer if it were more complex than "Kill everything" and "Form a Hippy Commune".
So why are the choices in these games usually between moustache twirling puppy kicking socio paths with big neon signs saying "Evil!" flashing behind their head that would soon as tie you to a train track as look at you, and angelic halo wearing sickeningly good pushovers that will do anything anyone asks of them even regardless of the cost often ignoring the greater good (mass effect has a good example of this towards the end).
I guess it is far easier to work in these caricatures than anything more complex. These basic cardboard cut outs are easy for the player to recognise (while a little tough for them to identify with since they are usually vacuums personality wise) and the story can easily be polarised down the good evil axis.
But what about something more sophisticated, people have tried various experiments along the lines of more complex stories but not many of them have worked. Branching story lines is one approach to this problem but tough to do convincingly and time consuming since each branch requires more work so there is a tendency just to make the branches the same or going for the multiple ending option Bioshock took. The Multiple ending approach was very popular back in the heyday of full motion video adventures, one of the early 3d attempts at an adventure game the Pandora directive had 3 different game paths with a possible of 8 different endings including my favourite the main character becoming a down on his luck alcoholic clown. Some of the more advanced almost AI approaches to this sort of thing lack the controls to tell a coherent story.
Of course for the most part those sorts of adventure games only really have their story as their selling point so it is easier to indulge in a little work to make a more complex plot, now that the focus has moved to a more action based approach I guess it is easier to let the story take a back seat or mover to a very clichÃ©d approach to storytelling.
With the whole move towards the open world or "GTA" style of game you'd think there would be more possibilities to have more involving more branching stories. A lot of the content they create in these games (like GTA and Oblivion) is never played they just do the main story and piss about with a few of the side missions then leave the game you'd think they could have invested the time to make all that stuff in making a more complex branching story line using their dynamic city/world as a back drop.
What would a decent approach to the whole good evil path thing be would having more appropriate shades of grey help where you can be just a bit of both or more manipulative than really evil. Maybe some of the problem of not being able to be a believable bad guy stems from the hero obsession either the games are written for you to play the hero with the dark path tacked on afterwards or the whole single hero theme really works against an intelligent bad guy. Maybe a game where you are the heroes sidekick/advisor would work better where you are there to sway their judgement and either betray or defend them for noble or more malevolent goals. I'm not sure anything like that would sell though which is the other problem most of the genre of games where this sort of thing fits is somewhat niche (or nitch as the americans say).
Will we ever see a game that intelligently handles the good evil path, I hope so. Until then I've got a moustache that needs twirling and a crate of puppies that need a good kicking, MWHAHAHAHAHAHAHAHAH!