This is idea came to me out this thinking that at this point, any sort of a return to the original type of gameplay from Fallout 1 or 2, is going to effectively be a spin-off. This got me to thinking what other avenues might be open to expanding upon the Fallout Universe with various gameplay formats and genres.
If you think the entire concept of a spin-off is just the worst thing that could be done to the series at this point, that's fine. But I'm not terribly interested in debating that issue with anyone - there's no middle ground to be found in what is certainly a subjective opinion - so there's really nothing I could add to the statement that "a spin-off is a horrible idea" beyond "I feel otherwise." Feel free, obviously, to post opinions about any of these ideas or what others may come up with. I just don't want this topic to devolve into a cyclical debate about whose opinion is "right."
That said, here's a few of my ideas:
Fallout: Back to Basics Basically, a return to the original Fallout format. With or without 2D sprites and an isometric view. Basically an RPG with more traditional RPG mechanics in mind. Personally, I think the DS could handle something like this pretty aptly (I'd imagine you could easily fit all of Fallout 2 on one DS cartridge at this point) but it would on a PC interface just as well, of course. If we went the PC route, I'd like to see some current-gen 3D graphics involved - and I think a turn-based game with lots of pretty graphics could make for some very cinematic combat, as well. Anyway, this one's sort of a no-brainer, as well.
Fallout: Tactics Another no-brainer, pretty much. Not that much different from the original RPG, really - only with more of an emphasis on squad-based combat and leaner on the role-playing front. I think there's likely a pretty interesting story to tell in how Lyons got his troop of Brotherhood all the way out to DC. And this sort of game would be a good fit for telling that story, I think.
Fallout: Wasteland Chef This is along the lines of me trying to think of something that'd be a big departure for the series, but at the same time incorporating key themes and using those to add some new twists to a different genre. Basically a cooking/ restaurant management sim - creating and following recipes to serve to people, while dealing with limited food stocks and trying to use your profits to expand your enterprise for the good of mankind.
You start out training as a Cafeteria Worker in a Vault, where you learn the basics of the game and some basic recipes. Eventually you are expelled from the Vault for being too experimentive, failing to stick to Vault-Tec Approved recipes, and creating un-Vault-like dishes that inspire rebellion and unclean thoughts among the populace. Stranded and alone in the Wastes, you are discovered by a group of travelling nomads and nursed back to health by their unorthodox and inspiring food. They impart in you the concepts of minimizing food waste and creating recipes that are efficient and use every bit of food available - as well as acting as a tutorial and giving you hints at making up your own concoctions.
You make some life-long friends, and together you decide to set up your own business at the bub of a major trade network. There's already some competition within what are the beginnings of a permanent settlement, so it's up to you to draw business to your place from the merchants that pass by, bartering your services in exchange for more food and supplies to build up your place and upgrade it with things like better stoves, more seats, a working icebox, etc.
As you expand your business, you have to keep track of your food stock through intermittent shortages and learn to improvise with what you have. Elements could potentially get very detailed, down to choosing what you do with each part of that Brahmin you managed to get your hands on - do you throw out the hooves and other unsavory bits, or work that into a recipe as well? Also, managing your business and hiring more help and enlisting the aid of helpers to scavenge more food for you. Build up a reputation and curry favor with the locals by learning their favorite recipes or comping their meals on occasion to unlock more upgrades and earn a bigger share of market in town.
As your business increases, so too does the town grow in size to give you a constant challenge. Deal with various events like raids and Supermutant attacks, and respond to the shortages these cause. Your final challenge comes when the area experiences a great drought and you have to manage to keep the entire town fed and their spirits up by making use of your constantly dwindling supply of food. (You've run out of brahmin meat - do you decide to serve cannibal dishes as a last option, or make due with what little you have left?) Win through to the end of the bad season and you're the hero of the town (with various endings depending on what sacrifices you've made with your morality during the crises.)
Fallout: Around the Wasteland in 80 Days A racing sim. Learn the basics of the game practice your skills doing missions in a hub-type city (starting possibly with riding horses or brahmin around, working your way up to cobbled-together motorcycles, etc.) Then participate in an endurance race to uncover a fabled pre-War artifact. Customize your ride, and struggle to keep it well-maintained for as long as possible - always on the lookout to scavenge more fuel and spare parts. Combat others trying to get there before you, and steal their transportation.
Fallout: Doomsday A classic point-and-click adventure game telling the story in a more cinematic manner of life immediately before, during, and after the War.
Fallout: Vault Overseer This is another one I think is fairly obvious. A sim-style management game where you construct Vaults for various experiments and then do your best to keep things running smoothly. Weed out unsavory elements by making them dissapear or fall prone to "accidents," keep everyone happy, and hope you remembered to stock up on Water Chips.
Fallout: Wasteland Minstrel Surely something that is in high demand in the Wasteland is good entertainment to keep people's minds off the harsh realities of existence. A music rhythm game (compatible, of course, with Guitar Hero and Rock Band controllers) where you travel from town to town plying your trade in exchange for food and shelter. Fend off attacking raiders with your awesome drum solo, tame the savage Deathclaw with the sleepy tunes of your guitar. With the ultimate goal of garnering the favor of a powerful radio station and using your skills for the betterment of the human race. (And with new controller add-ons like the Jazz Piano and Pre-War Violin, of course.)