I've just started the sixth season, so my opinion only reflects on what I've seen so far, and that's a -for me- very disturbing mixture of enjoyment and annoyance.
Since everyone knows the show's strong points (and there are quite a lot of them!), I'm not going to talk about those. But there are things that are portrayed -and perceived- as good, new, fresh, etc. that are actually really disturbing elements.
There's the obvious "new": Nerds as main characters in a popular sitcom. But no matter what you think makes a person a "nerd" (history nerds, science nerds, pop culture nerds, gamer nerds, socially inept losers.. ._.) it is obvious that the show doesn't have the audience laugh with
Howard, Leonard, Raj and Sheldon. I'm too lazy to get into detail, but this is something that really bothers me.
Then, and I'm not sure what to call it (sexist?), we have Penny. Penny doesn't have a last name. She's mostly used as a writing device, as Leonard's love interest, as someone Sheldon can be arrogant at, etc. She's never really a person- And then there's her and Leonard's relationship, which is cringe-inducing. The narration is incredibly Nice Guy, with Leonard even saying things like "I was nice to you because sex", and everyone nodding along, because Leonard is such a sweet guy. Really? (Bechdel Test? Probably failed. So far, I'm not sure if there have been two women with full last names who talked about something OTHER than a guy. Might have missed it, though.)
Other issues I have are consistency (cat allergy? belts?), the constant not!progressive gay-baiting, and most importantly the way the show/characters treats Sheldon's autistic behaviour and asexuality.
Don't get me wrong, I enjoy watching the show. I laugh, there are episodes that I've given 9+ stars, and episodes I've watched more than twice, but there is always a little voice in my head that points out all these things. And I can't help but think: The fact that those are "little" moments, moments that are easily missed, hurts even more.