This happens a lot with me. I've got the attention span of a small rodent most times. "Yeah, this game is awesome! I just found a new chainsword, new armor, now I'm gonna...OOH SHINY!" Then I put the game down for a while, and the death spiral begins. After a few weeks, I think "Oh, I should get back to that one." Then I think "Huh, I was about halfway through, and the missions were starting to get tough, and now I can't remember any of the controls." So I put off playing. A few weeks later, I have the same thought, except now I remember even less of the controls, so I wait again. Then it's a year later, and I barely remember what the game was about in the first place.
Most games these days start out with a tutorial. This is because most gamers are too lazy to read the manuals now. I'm not one of those, but publishers have realized that manuals are a waste, so most of them barely even include a manual. Hell, most gamers are too lazy to read two sentences on the screen, so designers have to figure out how to teach them using flashing lights and pictures. Yup, most gamers have to learn games the same way that you teach first graders to read.
After the tutorial, most games gradually ramp up the difficulty over the course of the levels, and usually add in new stuff. First you learn to jump, then how to swing a sword, then how to do a jumping slash, etc. By the middle of the game, the levels are designed with the expectation that you know how to do Things X, Y, and Z.
So what happens if you stop playing for a while, forget Y and Z and only have a hazy memory that X involved the A button? Well, most times you flail around for a while, probably get killed a few times, and hopefully most of it comes back to you. If not, you maybe consult the interwebz to figure out what you forgot. In extreme cases, it may be more worth it to just start over.
Here's where the re-torial comes in. In most serial TV dramas, there's a "previously on" to remind you what happened before since they know not everyone (who's not insane like me) will remember that tiny detail from three weeks ago that's about to be important. I want that for games too.
All the current consoles keep track of what day it is, and keeping track of the last time you played a game is pretty easy. What if the game checked how long it's been since you played last, and if it's been more than, say, two weeks, would offer you a recap? This could be both for the storyline and for controls. You set it up as a training room kind of thing, a menu of different moves you could re-learn, or a really basic mission to mess around in without interrupting your conquest of the universe.
Now, some games already offer something like this. At least a few RPGs have a "recap" section in their quest journals, and that's great. Other games offer a help section in their menus that lets you replay the tutorial sections, and that's also great. The game Alan Wake, already set up like a TV series, does a recap at the beginning of each chapter but, bizarrely, doesn't play it at the beginning of each play session.
So if you're making a game, remember us ADD gamers who might put your game down for several months, and give us a way to ease back in after we've forgotten how to play. I hate mixing up the button for "duck" with the one for "stab dude in the face so he doesn't kill me".