I like the Big Bang Theory, but I don't relate to Penny at all. I relate most to Sheldon, because he doesn't comply with social frivolities. People see him as annoying, but its him just doing what he wants to do. I can see why people wouldn't like the show...much of the humor is based on the characters, so if you don't buy into the characters themselves, the jokes alone aren't that funny.
This is where I disagree, there is no depth to any of the characters on TBBT, it's their persona you are laughing at, or the creators portrayal of the "nerd" persona. Like I posted earlier, it's only funny to people who aren't nerds, but know a few. They hear them spew lines about the nerdy things these people do, whether it be their profession, hobbies, video games, etc. follow it up with a 'bazinga', ???, profit. Seinfeld, Curb, Sunny, those are all shows that actually build upon the nuances of the characters themselves. You will see references to the character development of someone like Dennis in season 2 all the way down the road in season 8, while TBBT maintains a serial nature where you are supposed to wipe your memory clean that each character exists from episode to episode each week.