Really? We've had decades of absent-minded professors, mad scientists, and nerds complaining about their childhood treatment and taking their revenge on the world. Now that is something we might complain about.
But Big Bang Theory? Please. Most folks focus on Sheldon, so I will too. Sheldon is portrayed as a good guy. That's right, he's shown very positively. Yes, he has difficulties with social niceties. But he tries. He really wants to learn how to interact with people properly. It's not his fault he isn't very good about it, but instead of making excuses ("I can't act nicer, I'm an assburger"), he tries to learn from his mistakes, learn how to recognize sadness and sarcasm, and react appropriately. When someone needs a large amount of money, he offers to lend it to them, for whatever amount of time they need it, interest free. When someone's feeling down, he tries to comfort them, even though he doesn't really know how. It's tough to attempt something you don't know how to do. But it's the right thing to do, and he tries. Even when it involves touching other people, he does so, overcoming his aversion to doing so. That sort of thing makes the character a good one, in my opinion.
"But they portray Sheldon as a buffoon!", I hear people whine. Really? Granted, Sheldon is often portrayed as a buffoon. But so is everybody else on the series, including most of the guest stars! Everybody's a little off in this show, it's part of the show, not an insult to anybody in particular. That was part of what I liked about In Living Color: they were evenhanded, making fun of everybody. I really can't object to that, as long as it isn't mean-spirited. And if there's mean-spiritedness in Big Bang Theory, I simply don't see it.
That's a subtle difference, and hard to point to, but it's important. Anybody remember The Man Show - the original one with Adam Carolla and Jimmy Kimmel? Lots of folks objected to that, saying it mocked women and objectified them, treating them as nothing more than sex symbols. There were a lot of such shows before, during, and after it that did exactly that (and I include the reboot of The Man Show with Doug Stanhope and Joe Rogan). But the original Man Show wasn't like that. The hosts (Adam and Jimmy) love and respect women, and I can see it in the show. A lot of their gags boil down to "I don't completely understand women, but I adore them". That's why I liked that show, and didn't really enjoy any of the others of that sort.
It's the same way with The Big Bang Theory. While the jokes necessarily revolve around the characters and their personalities, they're not mockery, they're poking gentle fun. And many of the gags are simply standard sitcom fodder - they're laughing at what it is to be human. And that's always going to be funny. If you've read Alison Bechdel's Dykes To Watch Out For, it has a similar feel. Yeah, a bunch of the characters are lesbians, and a lot of the story lines hinge on things lesbians do, say, and are - including some stereotypes. But the main message I get from the comics is "we're all human, and we all have the same sorts of fun, problems, and laughs." The same with The Big Bang theory - it's a show about being human, with the wrinkle that not all humans are alike. As someone who's "not alike", it's nice to see that explored, whether it's in a humorous vein or not.
And yes, sometimes I'll do or say something nerdy (like "I like to turn the plates so they face the sprayer in the dishwisher"), my sweetie will smirk at me and say "Okay, Sheldon!" It's not mean, it just reminds me that I can be picky about minutiæ. And it makes us both smile.