Spoiler Level: High
There are three things I love about Steven Moffat's Doctor Who stories:
1) His dialogue,
2) His appreciation for the entire Doctor Who mythology,
3) The way he uses time travel as part of the story, and not just as a way for the characters to arrive in the story.
Matt Smith's debut story as the Doctor had all of this and then some. The opening scene has got to be the best TARDIS crash scene yet. The post-regeneration humor had me laughing out loud. The time-traveling elements of how the Doctor met Amy were just wonderful. The first look at the new console room had me bouncing in my seat. And the debut scene of the Doctor in his new outfit is hands-down the best debut shot for a Doctor, ever.
The plot itself is a fun story, with a cool monster and even cooler aliens. The scene where that alien message started playing all around the Earth and I realized that they were referring to the Earth itself and not just Amy's house gave me chills. (Although it took the Doctor long enough to figure it out... maybe because he had just regenerated?) But as with most Doctor Who stories in the new series, it's just as much about the characters as it is about the plot itself, and this story successfully balanced both.
And Matt Smith nails it as the Doctor. I was concerned about him being so young, but I never even thought about it once. The way he opened the TARDIS doors with the snap of his fingers came across as so natural. I think he's going to make a great Doctor.
Okay, more about the new TARDIS console room. I love the balcony. Brings back the HUGENESS that you got with McGann's. I love the typewriter and pinball machine parts. I don't really care for the bulbs inside the time rotor, but I'll get used to that. All in all I feel like this one stays true to its roots and expands on what was started in the RTD era.
Steven Moffat's stories have always been my favorites, and this one is no exception! Long Live the Moff! Long Live Series Fnarg!!!!