This is certainly the most elaborate pony to come of G4! She lights up, sings, talks, moves her head, blinks her eyes, flaps her wings, and even has wheels subtly placed under each hoof so she can "glide" along. As you can see, Twillight comes with a comb (new mold) and four large barrettes (also new molds). Her crown and necklace are removable, and snapping the crown in place activates a special button that makes her talk.
I could go on for hours with all the little details, but I'll try to make this a comprehensive yet to-the-point review. :)
Also worth noting is that the mane is rooted into a section of plastic that moves slightly outward from the head when the hair is tugged. This is most likely to prevent stress on the head-turning mechanism during brushing and styling. An excellent idea that will no doubt extend this toy's life in many a home! I initially thought it might be another lights-and-sounds trigger, but I've been unable to get any reaction from it.
Finally, here's a video I made demonstrating all of her phrases, sounds, effects, and animatronics.
Bottom line: I truly love this pony. The artistic liberties taken with the character design work well and add to the aesthetic appeal, as far as I'm concerned. She has a few flaws, but you'd be hard-pressed to find a toy that doesn't. For a collector, she makes a lovely centerpiece to a MLP: FiM collection. For a child, buying this one is a no-brainer; I don't know what young fan of MLP wouldn't be delighted to receive this beautiful toy. :)