Sometimes I cannot come up with a rule system to use with a video game in question so I usually start thinking what kind of system I should create for it. The easy part is that video games are usually focused in a particular gameplay so the rules wouldn't have to be all covering. Just to do the things what in the video game happens.
Some of the games give inspiration to create house rules or custom classes for an existing game to emulate what happens in the video game. Here are some inspiring games I have wanted to run. In the end of this post are some reasons why I haven't done it yet. The first game in the list is:
Assassin's Creed 2
What could be more entertaining (in rpg) than to get to play an assassin in historical setting pursuing his cause killing people one in a time? And doing other things in between? Many things actually, but nonetheless this could be pretty cool.
Some D&D clone could work pretty fine. Roll d20 to hit when you are in melee and because of low HP in starting levels (gap to 6 or something not to make our assassin too powerful) direct combat is not an option you want to engage in. Sneak attacks and avoiding enemies is your goal to victory. Most of the Thief classes skills would be great for an assassin, but I'd probably go with Lamentation Of The Flame Princess' 1d6 skill system here. To keep things simple.
So, there's our assassin. Only bigger modification would be a counter attack. In Assassin's Creed you can counter attack enemy attacks what is nice feature in melee combat giving you an edge. In D&D clone I'd handle it this way:
When an enemy attacks and rolls 0 + assassin's level, the attack is countered dealing damage equal to the assassin's weapon in use.
So first level assassin's counter would occur on d20 roll of 1, second level assassin's on 1-2 and so on. There would be no limit on how many counters could happen in a round.
The rules are simple, it's the locations what matter. You'd need great city maps of different levels and layers for the game to be enjoyable. In the game you run the streets, climb the walls, dash through the rooftops and so on. So a detailed map would be a must for this.
Saints Row 2 & 3
In a rpg it would be cool to be a gang boss dealing with gang stuff. Doing missions to make his gang the biggest one. Action, drama, street politics, management all there.
I thought that modified (new) World of Darkness (core mortal) rules would be fine for this. Modified for faster approach. And stripping some skills you wouldn't need that much. Also WoD character advancement is slower what suits this game well. Also you could give some special powers for the player character using these rules.
The biggest new rule compilation would be gang domain and management rules. I did find ages ago rules for this on some blog, made a PDF of it (using Printfriendly) and lost it when my external hard drive broke in a thunderstorm! But there are gang rules somewhere. I probably could find those googling (if someone doesn't tell me what I am talking about here).
What you would need is a city map. Not hard at all. Just take something from google maps, layer some hexes or whatever and done. Hexes for areas and noting points of interests (gunshops, bars, safehouses, etc. you know). The I would laminate the map after printing it to use markers to draw all the gang districts on it. It would be easy to sweep markings and modify them.
One problem is that the player should be really engaged. Naturally a Referee would give stuff to do but it would be up to the player to manager his gang empire.
Anyways, as a rpg this would be like modern day Assassin's Creed. But as D&D clone rules would work fine with Assassin's Creed I don't think they would be fun with Hitman. Not sure what rules would, because Hitman is a badass. I thought a simple 1d6 system would work fine. There's a 3 in 6 change to hide from the police officers and the disguise gives you +1 to the change. Shooting that guy in the head so others don't notice it is 1 in 6 change but silenced weapon gives +3. And so on.
Hitman doesn't need stats. Because he can do what he can do and he doesn't do what he doesn't do. It's all x in 6 in this game.
The point is not what your character can do but how he will do it. For example if killing a baddie in the middle of the crowd unnoticed would be 1 in 6 change. So the player should be imaginative and try to create a better and more secure plot to get rid of him. Shanking him while passing by would be 2 in 6 but that's not good enough yet. Sniping him from rooftops would be 5 in 6 (someone might notice you still) and it would get the crowd hysteric but at least it would be better than other options. But how to get 6 in 6 change to kill him unnoticed? Well that's a task.
You need lots of maps for locations and lots of preparation for this one. Every mission should be a playground for the player.
Joining a video game is different than joining a tabletop pen and paper rpg. Video games are an experience of audio, visual, hand control and reflexes combined to a story and what your body and mind thinks is fun. Roleplaying games are mostly imagination and mechanics what your mind think is fun.
The problem here is that if a game is fun to play it is not only the story and the imagination part. It's also the controls and visuals. In roleplaying game (for me at least) what makes it enjoyable is how the Referee runs the game. Even crappy rules or a setting I don't like turns out to be good if the Referee is good. If a video game controls are horrible it most definitely will eat the fun. Or the controls might be super sharp but the story and visuals are lame and unimaginative. Those are big problems what leave video games mediocre - or even bad. A bad rpg can be good if the Referee is good.
So if the game is fun to play on a Xbox 360 it doesn't mean it would be that fun in a tabletop environment. In Hitman Absolution it is fun to sneak and successfully kill an opponent and repeat this for the entire game but in a tabletop it would be boring in the end. The game would need more to that.
Also it is damn fun to climb quickly towers and hastely run the guards through the rooftops in Assassin's Creed, but in rpg it would easily be a mess of descriptions or lame random rolls (last year there was a 1 page dungeon of rooftop escape, go check it out).
In video games there usually is a theme and gameplay you more or less repeat through the whole game. In Assassin's Creed you climb, run, occasionally fight, collect treasure, assassinate. Repeat. Hitman you sneak, observe enemies, assassinate. Repeat. In a roleplaying game Assassin's Creed and Hitman as would be quests or missions of few gaming sessions total of a whole campaign. Not a campaign at themselves. Well, there could be a campaign focused on these themes but to make it more interesting there should be more (actually some people have been in dem dungeons for 40 years now with same old rules and same old races as classes!!!).
What my point really is personally I think I cannot turn the experience I find fun in video games into tabletop gaming. I have used some inspiration of video games or even video game concepts in games earlier for a quest or some sessions. Not entire campaigns. You could make a campaign of Hitman Absolution plot as easily as you could make a campaign based on a book, film or a rpg campaign setting naturally but I don't think you can easily convert the mechanics and repeatition of the video game to be fun in a rpg.
For one shots sure, but as a campaign not sure. My shortest campaigns have been a little over 10 sessions and longest 200 sessions or so - over 1000 pages of text of actual play. 1000 pages description of Saints Row 2 gameplay would be exhausting.
What Do You Think?
Now, what do you think? How often you convert mechanics or ideas found in video games into roleplaying game mechanics or custom little games?
How often your campaigns are shaped around a video game?
When you run a game based on a video game do you capture the fun of video gaming in roleplaying or do you have to do compromises to make it work as pnp game?