I love this show. I resisted watching it for the longest time, then last year, I sat down and watched three seasons all at once. It is hilarious, very well written, has an excellent cast, and still continues to be a strong series, into its fifth season, which just began.
I love Johnny Galecki, ever since I saw him on "Roseanne", and am so glad he's on another long-running series that I love to watch. Bring Sara Gilbert and Wil Wheaton, among others, onto the show as guest stars just adds to the awesomeness of the show. I hope it either keeps going, or ends before it gets cancelled and has some lame butchered ending to the series.