Well, I think Fallouts "soul gameplay" does involve weird quests,strange animals, and funny surreal happenigs that make no sense(Which I imagine there would be in a post apocalyptic world, heck we already have some of those things now), but you should still have all this with the option of "Ultra Realism" when it comes to things such as being damaged by enemy fire or vice-versa(one vital shot and you die,shot to spine cripples you, etc.) as for aliens, they are not anymore stupid and unrealistic than a nuclear apocalypse, which at sometime (somepoint far, far in the future hopefully) will not seem very unrealistic at all.
First of all, Fallout is about humanity's lust for war (Try and guess why there's "War never changes" in the intro. It's not just a cool one-liner, it actually HAS a purpose), how society may function in a harsh, post-war environment and with a bit of gruesome, dark humor thrown here and there. This is what the original creators said when asked about describing the game, I am not making this up. I am trying to find the interview where this is stated, but it's kinda hard ATM.
What most of you may not realise, it's not about retro-futuristic, post-apocalyptic America. This was chosen only because fantasy setting was over-used at the time and devs wanted to be original. The game is about:
1) freedom of play - you can go anywhere and do anything you like, providing you survive it, there are multiple solutions to each task, diffrent character builds yield diffrent gameplay experience
2) mature, grim world with a lot of morality issues
3) simulation of Pen and Paper type of game
The rest are only additions. Sillyness was added by the people who later took over the franchise and should be limited to a minimum in the upcoming games.