I have observed a shift in the subject of the jokes from the beginning of the show to current episodes.
At first, geek culture was celebrated, each opening the crew showed cool science projects or an interesting nerd conundrum. Also, Pennyâ€™s superficiality was the subject of the jokes.
To the contraire, recent episodes show dumb & weird science projects which mock the silliness of the situation. The characters often seem to be carving for â€œdrinking and partying with the cool kids at the parking lotâ€ instead of criticizing its sense.
Penny is now sought out for advice and Leonard often seems to realize how he has â€œout grownâ€ his friends.
I feel that instead of a celebration of the interesting and cool stuff from Comics, videogames, science, engineering, etc. the show has become a realization of shame from the nerd characters.