I prefer the earlier seasons to be honest. The original feel of the show as I saw it, was about four socially awkward nerdy guys. When the relationship story-lines of Bernadette, Amy, etc., were introduced, it felt forced and unrealistic. The first season we saw Leonard having trouble finding his words when talking to Penny. However, in later seasons we see him doing dating different women. It just felt so uncharacteristic. He turned from this loner geek that hangs out with his buddies in to some sort of nerdy playboy. I'm all for character growth but I think the rate that he matured was way too fast and without any real back story. He scored on the hot neighbor, then a season or two later, hes seducing chicks all over.
Basically the first couple of seasons felt like a couple of geeks that the audience could relate to regarding their social awkwardness and shared interests. However, their lives suddenly turned into something that a geek could only ever dream of. Well that's my opinion anyway.