While the first season of The Big Bang Theory got off to a slow start and then steadily improved, the second season continues the parabolic rise in hilarity and rockets the show into the stratosphere, easily making it one of the absolute funniest shows currently on television. There is not a single episode in the second season of The Big Bang Theory that doesn't make me laugh out loud on numerous occasions, even upon repeat viewings.
In my review of season one I had a few nit-picks. The issue of confusingly-titled episodes (for example, "The Euclid Alternative" wherein Sheldon tries to learn to drive) still remains and will probably be in effect for the duration of the series, unfortunately. But, one beef that is totally resolved in season two is that annoying Sheldon is finally allowed to be vulnerable, making his character not only finally likable and relatable, but possibly the most likable of the series. Numerous episodes play on Sheldon's new-found vulnerability, to the extent in a Christmas episode where the nearly-robotic character just about breaks down in tears. Very funny and earnestly touching tears.
It's also worth noting that Sheldon attempts smiling for the first time this season, with hilarious results. Reacting to Sheldon's first toothy attempt at a smile, Leonard quips, "We're here to see Koothrappali, not kill Batman."
The writers and cast really hit their stride right off the bat in the second season, following up on Leonard and Penny's date from the end of season one. Of course, things don't totally work out (after all, we all know the castaways aren't going to get off Gilligan's Island right at the outset; these things need to linger for the show to work), but it becomes obvious that Leonard isn't the only one who seems to want the relationship to work. This is followed up in a later episode where Leonard gets a steady, live-in girlfriend, and watching the jealousy that emanates from Penny, and the reverse jealousy from Leonard, makes for some very funny scenes. The tables are turned again at the end of the season when Leonard must cope with Penny's interest in one of Leonard's nerdy comrades.
A big and very welcome change from the first season to the second is that Penny is no longer simply the stock blonde bimbo character living next door. She is now officially ingrained as one of the nerdy group. (The episode where she becomes addicted to MMOs firmly establishes her as possessing the ability to be even nerdier than the guys.) Best of all, she's been integrated in so fully that she can now playfully bust the guys' chops a bit, even Sheldon's. In fact, the best scenes of the season occur between Penny and Sheldon. The writers discovered just how well these two characters work together, and seem to go out of their way to find scenarios that would delightfully play these two off of each other.