Sorry I'm late to this thread (so-so Newbie - that's my excuse), but it deserves a bump up.
Missed all the debate about what's good, what's bad and people dissecting it too much - just enjoy it for what it is. A damn good sitcom.
Age/male/female appeal? Well, I'm let's say a retired old fogey and both I and my 30 year old daughter have thoroughly enjoyed this from day one.
Without the introduction of Amy I think, as someone has already stated, it could have gone stale and in my opinion she has been brilliant as the frustrated female nerd who lusts after Sheldon and envies Penny her carefree life style. I was doubtful about her when she first appeared but has certainly added a new slant.
My only reservation was when Howard was up in the space station. I didn't think it worked at all and got too far away (!!) from what made it good with them all interacting with each other. Also, presumably the baseball cap was to get round his wig floating off in the cabin! But the episode when he came back to Earth put it all back on course. Loved it when he said he was going to have to change his dentist!
Absolute favourite skits:-
For me it was the Christmas edition when Penny got the Leonard Nimoy signed napkin. Sheldon's reaction was classic and had me falling about laughing.............and still does!!
(Point here - I wonder WHY they don't get him in a cameo role? It would be fantastic!!)
Oh, and when he got involved with advising customers in a computer store. "So, what kind of computer are you looking for? And please don't say a white one"
My daughter's favourite was when Sheldon bought Amy the tiara. Perfect timing, how she went on about him trying to "bribe" her with a "sorry gift", and then she unwrapped it. Brilliant!
Now we've got past Howard in space the current series is maintaining its superb comedy.