Penny getting pregnant isn't that odd, given the first episode. I've seen lots of comments about Penny not wanting kids, and being annoyed the show had her get pregnant anyway. It's not unusual for a woman to change her mind on that issue. I've been married over 40 years, and had a few friends who started off adamant about not wanting kids. Most of them ended up with a couple of children, happy they hadn't stuck to their first view. People change as they go through life, decisions made as young women don't always remain the same as life happens.
I wasn't thrilled with Amy's makeover...it didn't seem real to me at all. It was too much of a change all at one time. Amy would have been totally uncomfortable in the new clothes, especially the spiked heels and low cut dresses. It also fed the idea that women/girls have to look a certain way to gain acceptance, aside from the fact that she just won a Nobel, an accomplishment that had nothing to do with how she looked. It didn't feel right to me.
Raj...wow, total dis to the character. Boo hiss. I get the tie in with Buffy, but not for Raj. He wasn't the one who wanted Penny to love the show. It felt mashed in for the sake of tying it to a past show, with zero ties to Raj. Why not bring back one of the cute gals he dated, with some grand romantic gesture for him?
I loved Stuart and Denise together...some little nod to them would have been nice, beyond the incompetence.
I loved Sheldon's speech, it made my eyes puddle. Overall it was a pretty good ending, and well past time I think. The show had been feeling a little forced.