Maybe this has been discussed before in the forums, but I thought it was an interesting topic. For a long time, I've been thinking about how to implement a romance between the player character and an NPC in the game that I'm writing.
I've replayed some old games, and so far I haven't found a succesful example of it being done. There seems to be a number of approaches, most of them pretty stereotypical:
1) Player character in a relationship when game starts. Phantasmagoria 1 and 2 did that. Police Quest 2 and 3, and I suppose, a couple of the Larry games. Rise of the Dragon did it pretty well, as far as I recall. Often the love interest is used as a plot device (Damsel in Distress - if there is a girlfriend, she's bound to be kidnapped at some point) or just as a means of establishing the more emotional side of the toughguy detective. Steve Dorian in Dagger of Amon Ra, probably the most ridiculous love interest in any game (and not just because he's a guy), has a damsel in distress role as well - the trouble being that you hardly even know him and don't really care if he should step on a poisoned nail without his boot on

.
2) The player character, for some weird reason (Love at first sight, destiny, magic) falls in love with some complete stranger, and pursues them either to the end of the game, or at least for a while. Sometimes the object of affection is the goal of the game (KQ2 and KQ6 come to mind), or a means of getting the player character further involved in the plot (Gabriel Knight). Monkey Island did this too with Elaine, but at least they tried to make her likeable.
3) Player character and love interest work together throughout the game, and - of course - have a love/hate relationship. Think Cybil Shepard and Bruce Willis in Moonlighting. Gk2 and 3 had plenty of sexual tension between Grace and Gabriel as did the Broken Sword series with George and Nico. Oh yeah, not to forget Indy 4 with Sophia.
As far as I know, very little has been written on the role of character interaction in graphic adventures as opposed to in IF (where dialog alternatives are much less obvious than in point and click. But I suppose it's related to different views on the player character: Is the character an avatar, a tool for the player to interact with the game world, or is he a role that the player is trying to act out, a character with a preset personality and emotions beyond the player's control.
Should any romance be written as a potential rather than a fact? Should the player be able to choose whether or not they would like to pursue the relationship? How much interactivity is needed for the relationship to seem plausible? I hated the way GK1 just assumed that I would understand Gabe's attraction to Malia. But I see how it would be extremely difficult to tell the story if the romance was optional.
Also, I would like to hear your thoughts on how romance and courtship should be "played out". Most games seem to deal with it as a simplified seduction, usually consisting of giving the right item to your object of affection - love as market economics. I don't even want to mention the Larry series, but even a lot of more serious games let you buy flowers or jewelry to convice the person of your feelings. Quest for Glory 5 was really bad in this respect.
But in what other ways could you imagine romance told through player interactions?
I think the most interesting romance in any game I've played was between Gabriel and von Glower in GK2, because it was an attraction between equals. And the NPC wasn't passive, quite the opposite, he was the one seducing Gabe. The only trouble was that this part of the story was only told in cutscenes. The player never had a choice. And I think that made it less powerful - because the theme of the game was very much one of choice, of following or repressing your animal nature.
The approach that I've currently chosen (but the game is still only in the design phase, so it could easily change, should anyone come up with something better), is - as in GK2 - for the NPC to be interested in the PC from their first meeting. This won't be a seduction subplot. The interaction will consist in the PC choosing, or not choosing, to open up to and let themselves get involved with the non player character. The player will have multiple choices - dialog options, actions (such as choosing to go or not to go to the NPCs party). But none of the available options will be out of character. The romance isn't part of the major plot, so it won't cause trouble with branching plot lines. It's used to reflect the state of mind and the growth - or lack of evolution - of the player character.
I'd love to hear your thoughts on this.