The problem with TBBT is that the writing of the last season(s) is so bad and lazy, that you are wondering why you liked it in the first place. Same thing happened with Two and a Half men. The decline in the writing of both shows coincidences with the introduction of their 3rd show, Mike and Molly.

It's a comedy show, you are supposed to laugh at the characters. None of them should be taken seriously, they consist mostly out of randomly selected quirks that change with each episode. The 'normal' people are just as silly as the nerds. If we were meant to relate to someone, it isn't Penny, but Leonard.