Play stlaker if you want a dry, realistic survival game.
Actually, I wouldn't call S.T.A.L.K.E.R. a realistic survival game, while it lacks some of the more far-fetched aspects of Fallout, mostly because it's not inspired by '50s science fiction and it's in a nearer future, I don't think you'll see too many mutants that can turn invisible, muntants that appear as nothing except a distortion floating around in the air and throw stuff at you with telekinesis, and gravitational anomalies that crush you or svck you in if you step in them. Still, S.T.A.L.K.E.R. is pretty different from Fallout, and while there may be some things Obsidian could learn from that game, I definately don't want Fallout to be like S.T.A.L.K.E.R. (Okay, if I ever need to use that name in this topic again, I'll just copy and paste it.)
but it's not a place where girls wearing pink dresses and armed in japanese swords should run around doing more damage than a PA-wearing soldier with a minigun (a real situation from Fallout 3).
Considering that I don't recall any pink dresses or "Japanese swords" (I like how you make it sound like there's only one kind of sword in Japan, although some writers of fiction seem to really believe that's the case.) in the default game, so you're probably talking about something added from a mod, and it must be said that players can add whatever they want with mods (within the limitations of what's possible in the engine, anyway.) and pretty much every game that has ever been heavily moddable has likely had some pretty silly things added by mods.
However, it seems to me that, at least for serious fans, the players asking for realism are mostly talking about realism in gameplay rather than in setting. It's possible to have an unrealistic setting in the game while still having realistic gameplay, as well as the opposite, you can create a game set in a futuristic world, with robots, aliens and mutants, power armor and what not, but still have everything behave exactly as you would expect them to in real life, likewise, you can have a game set in a relatively realistic world. Taking place in a modern city, with vehicles, weapons and so on that, if they don't use real names, are based on real ones, without any sort of science-fiction or fantasy themes, but still make the gameplay very unrealistic (The GTA series comes to mind, and the non-interactive varient often shows up in action movies, where you'll get people doing impossibly cool stunts with guns and vehicles that if they don't kill you in real life would probably be very impractical, and with cars exploding all over the place and so on.) To a certain extent, I wouldn't mind this kind of realism, but with that it's also important not to take it too far. After all, I play Fallout because I want an entertaining experience, not because I want an accurate simulation of what life in a post apocalyptic world would be like. Sometimes, a bit of realism can add to the entertainment value of the game, and as much fun as it would be to watch, I don't really want my attacks to throw enemies across the room, smash them against the wall with a loud crunch, cause them to cough what seems like more blood than they should have in their entire body out of the mouth, and then stand up and fight again. But too much realism would simply make the game boring, and if I really wanted full realism, I'd play a game where that's actually the point.
As far as the world is concerned, I think that Fallout fans mostly want internal consistency. In fiction, when it comes to crafting a believable world, this is often more important than realism. As an example, let's take a hypothetical fantasy world. Fantasy as a genre tends to be fairly unrealistic, that's the point of it, it's about crafting a world that is
not real. Whether this world is some fictional world in a universe completely different from our own or if it's a side of Earth hidden away from our every day lives, so therefore, it can get away with a lot of unrealistic things. Fantasy will often involve things like magic and a surprising mix of mythological or made up creatures, fans of the genre can accept these things. Now let's say you're reading your favorite fantasy novel, the author created a detailed world, with clearly defined races, nations, cultures and so on, maybe the author even defined rules for how magic works. But then when you're reading through the book, the wizard suddenly uses a spell that completely defies how magic is said to work in the setting, or maybe the villian has the heroes trapped in a situation where there's no hope of escape, and he decided NOT to spare them so they can come back another day or use an easily escapable deathtrap, and just starts executing them, then suddenly aliens appear out of nowhere and shoot the villian and his minions with lasers. You'll probably suddenly find that this is a pretty hard hit to suspension of disbelief, not because the idea is any more unrealistic than anything you've already seen, but because it clashes with what's already been established about the world. I'm perfectly fine with seeing super mutants, laser guns, and power armor in Fallout, because those are already established aspects of the world, and taking them out might actually ruin it. But I don't want to see elves using magic and wearing dark spiky armor with glowy parts come out of nowhere, those can stay in fantasy.
Oh, and for the record, I don't want to see any more aliens. Not because they're not realistic, but because they're not what the Fallout world should be focused on. Aliens to the degree they were presented in Mothership Zeta are more of a distraction from the things I like about the Fallout universe than an addition. Don't get me wrong, MZ was fun as a sort of "Easter egg" DLC, but no more, please.
Those are my thoughts too, actually. In fact, aliens really aren't a very unrealistic idea, the reasons for that I shall leave for the "Do you believe in aliens?" threads that sometimes pop up in Community Discussion, but I won't go declaring a science-fiction story unrealistic because it has aliens (although if we ever encounter aliens in real life, I doubt they'll look anything like what we saw in Fallout 3, but science-fiction writers don't need to let such petty things as biology or logic get in the way of crafting an interesting story.). And also, the occassional hint of aliens did show up in earlier Fallout games (The alien blaster, for one thing.) they're just not the main focus of the world, and shouldn't play a major role in future games. I didn't object to the crashed alien spaceship, the Firelance, or even the reference to aliens in one of the Pentagon terminal at all, Bethesda should have just kept them to easter eggs like that.