The four point-and-click adventure games are: The Blackwell Legacy, Blackwell Unbound, Blackwell Convergence and Blackwell Deception. As I said, I've only finished the first two and am halfway through the third game so I can't really talk about the last one.
Okay, so the major aspect of the Blackwell series that is worth duplicating is its premise. A single character (generally Rosangela Blackwell) must help ghosts move on by helping them remember who they are and that they're dead and her only assistance is a ghost who can't touch anything but can blow a slight breeze and pass through solid objects. Unfortunately, that ghost also can't range far from his medium. In the second game, the ghost became a playable character.
So how do you run this?
Well, you're best off keeping the game down to one or two players for a number of reasons. A small game allows for a more personal experience. The investigations would probably become too simply - or too complex - if you had multiple people trying to question the ghost. It just seems weird for four people to turn up to gently move a single ghost on. And that if you want to let someone play the spirit guide, you'll have a hard time giving him anything to do if you have a range of breathing characters with a range of skills who could find ways to bypass the spirit guide's spot light time.
You could have one or two medium characters and either make the spirit guide an NPC (Non-Player Character) or you could allow one of the players to be that spirit guide. A really interesting way to do it would be to make the medium the NPC and have the spirit guide advise them and try to find their own ways around certain situations but be aware that this will suit a more cerebral player over a dice rolling player because, well, the spirit guide can't do all that much.
I suppose you could give the spirit guide greater powers such as allowing him to drop the temperature in a room down to freezing, use telekinesis on objects, or manifest in front of people, and if you have the right sort of player and apply some restrictions on the powers so that they don't become super powers, it would probably work out. However, let's focus for a moment on how to make it fun for someone to play an incorporeal ghost while the other person plays the medium.
Firstly, encourage the spirit guide's player to make the ghost pretty interesting and entertaining to play. Joey is a wise cracking, somewhat cynical, and very playful ghost who likes to make a lot of chauvinistic comments although there's no sign (thus far) that he actually thinks that women are inferior. It's just that he likes to refer to them with phrases like 'baby doll' and tease his medium whenever he can. This ensures that simply playing that ghost can be fun and also opens up other opportunities for them to interact with the scene while the medium gets to actually talk to people. So what if the ghost oggles the pretty witness? If it entertains the players and is in-character, then that's great and works a lot better than if the ghost is a mopey fellow that rarely gets to do anything at all. If anyone is to be the 'straight guy' of the duo than it really should be the medium so that the ghost can play off of them and nab the limelight through humor.
Secondly, ensure there are spots where the spirit guide can excel. Ghosts who won't acknowledge the medium or who confuse her for someone else so that the spirit guide has to interact them for the story to progress. Animals that bark at the ghost or run away in fright. Papers that are out of view for the medium but which the ghost can just float around to take a look. Conversations that can be eavesdropped on from close distance by the ghost while the medium is waiting just within range (if doing this, take the ghost player aside so that they can report it in character and therefore feel all the more useful). Distractions caused by static-filled radios or televisions whenever the spirit guide comes near. Tiny objects that can be blown in a puff of air. And also remember that no one else can see the spirit guide so they can advise the medium regularly: "Say this" or "Do that".
Thirdly, give the spirit guide a better understanding of ghosts, mediums, and other important tidbits. Preferably by taking the player aside and explaining that this is how this game will work and these are what spirits are like so that they can make educated guesses on how best to deal with them.
Sometimes even Joey can be chivalrous.
Remember that you'll need to put in extra effort to keep the spirit guide relevant. Because of this it's also worth-while double checking with the player if they actually want to play this. Some players can take it and run with it - especially those with tactical minds - and will find plenty of ways to stay relevant and gain a real sense of accomplishment. Others (dare I say most) will find themselves easily frustrated and often stumped while the player of the medium gets to do most everything.
It's also a good idea to get the medium's player on side to come up with ways for the spirit guide to be relevant. Sure, the medium *could* grab the note and run off with it but why not just let the spirit guide take a look at it? I'd suggest that to support this, and the real teamwork vibe of the Blackwell series, that you award bonus experience according to times they worked as a team or bounced off each other as well as times they came up with ways the *other character* could be useful.
After saying all that, though, you could end up having a fantastic game where a player gets to run around as a ghost. It's just all in the pre-campaign prep work.
Okay, that aside, what else would you need?
Well, it'd help to have ghosts that you can't kill and which, ideally, the medium can't even touch. This isn't meant to be like the hit tv show Supernatural where you can swing an iron pike through a ghost and discorporate it. The ghosts are non-violent. At worst, they can be summoned via ouija boards to plead in the ears of the living until the living choose to die rather than hear it any longer. True, that's a pretty big 'at worst' but it's a far cry from murderous ghosts.
The gameplay here revolves around locating the ghost, figuring out who they are, learning more about their background, and finding some clever way to help them remember what happened to them so that they can regain their mental clarity and cross over to the other side. During these investigations many other things may come to light such as normal, mortal crimes like murder or robbery.
The main part of the puzzle here is finding the connections between clues so that you can ask people the right question. This may involve noticing a ghost's picture on the wall, tracking down their neighbors, or locating cash to bribe somebody. It's less about literal puzzles or finding the right object to solve the right dilemma and so the actual gameplay can actually be duplicated far more easily in a pen and paper roleplaying game than is generally the case with adventure games.
A campaign based around the Blackwell Series, or including elements of it, should appeal to Investigators who would enjoy all of the background searches and piecing together the different clues to form a picture of the past. Communicators will likely enjoy the focus on the human element and may like to also look at stories following a day in the life of a medium where they just try to get by without being heckled by their ghost too badly. Explorers would be more keen to explore the world of ghosts and would probably be hopeful to explore some aspect of the underworld. You'd need to ensure they have ample opportunities to visit strange places and break into locations to keep them happy.
Tacticians could do quite well for themselves when it comes to using the corporeal and incorporeal investigators to their best effect. Action Heroes are unlikely to get the high adrenaline excitement they generally crave and may get quite bored with the slower pace.
There's no trailer for any of these games although you could look up the Actual Plays on Youtube. If you'd like to read the sort of tropes that the Blackwell series used, you can find them here.
For the next Game Translation, you have a choice of these: Left for Dead, Half Life 2, Metro 2033, Skyrim, Gears of War, Mass Effect, Dracula: Origins, Realms of the Haunting, Dragon Age 2, and pretty much any survival horror or horror game. If no one picks anything by next week, it'll be Metro 2033.
If you want to see the list of games I've done thus far, you can find the Game Translation series starter over here.