there is humour at every level in the show - which is why it's successful. there are nerd jokes in there that would go over the laymans head (and if you don't think that there are, then you're a closet nerd and got them or you missed the jokes... and this isn't just talking about intelligence levels, but also nerd and gaming culture, too). this is particularly true of earlier seasons. there is also plenty of relatable humour for most anybody else watching the show, too... right up to and including "i don't really understand what is going on, but LOL@NERDS".
for example - what percentage of the population do you think understood the Doppler Effect joke, immediately when Sheldon was dressed as it? then how many when he tried to actually explain it to the party-goers in that episode? i'd wager there are people that have seen that episode that still don't know what the Doppler Effect is, even after Sheldon explaining it in plain english.
Kaley Cuoco is also very easy on the eyes.