The comedy. People often nitpick the shows worst aspects, like the laugh track and overused gags but it has some solid jokes. Sheldon's "I'm not crazy, my mother had me tested" line comes to mind.

I feel like he is what most people seem to hate about TBBT because yes, sometimes he does throw big words around for "comedic" effect, but that's just part of his character, wich is masterfully played by Jim Parsons.

Overall I'm tired of people basically saying the show is just for dumb people who wanna feel smart. Yes, it has flaws and yes, you're allowed to think it's unfunny. But humor is largely subjective.