I agree with Josh (aside from his parallel with film, to have a valid opinion that you use in a review or argument, you need to watch a film in it's entirety) To know if you like a tv show, 2-3 episodes is all you should need (unless it's a particularly story heavy show that runs with one arc an entire season, then you should give it a few more episodes). I really didn't like Community after watching the first episode, but since it was on Thursdays and I was going to watch the other three shows on that night, I gave it another chance. By the third episode, I loved it, but had I still not liked it by then, I wasn't going to.
If you don't like a sitcom after 2 or 3 episodes, you just aren't going to like it and that's more than enough to write a review on it.
That being said, I do enjoy BBT. It's not particularly smart, but it's fun.