Well it wasn't a bad episode but I don't plan to watch it again anytime soon. It did have some pretty good moments though, like:
Pinkie dumping flour all over her. I'm glad to see I'm not the only one who thought of Surprise when she did that.
The rubber chicken Pumpkin Cake was sucking on. Dragonshy anyone

?
Diapered Pinkie Pie. Glad Fluttershy wasn't there.
Pony genetics sound pretty interesting although they don't make much sense.
The horror movie bit near the end was really funny and quite clever.
One thing I really didn't like was the design for the twins. Now I don't think they looked as bad as the baby in Mare Do Well but they still weren't too appealing to look at.
Going back to the pony genetics, like I said, it really doesn't make a whole lot of sense. While I suppose I can (somewhat) see how Mr. Cake could produce a unicorn which I guess could be a dormant gene if we assume that his parents, grandparents, great grandparents, and so on leading up to the unicorn great (insert number of greats here) grandfather were earth ponies, I don't see how Mrs. Cake could have a pegasus. How does her having a great aunt second cousin twice removed (Wut) make it possible for her to give birth to a unicorn? Maybe I'm reading too much into this.