Episode 1: The Impossible Astronaut
Starts things off with a bang (rather literally). The word "impossible" in the title is well-deserved: something you would never have expected to happen really does. Feels more like a typical DW series finale in scope rather than a premiere, and makes for a nice change from the norm. Lots of new plot threads introduced, some new development added to old ones...including the revelation of the Silence, definitely the scariest monster Steven Moffat has created so far.
Episode 2: Day of the Moon
It's hard to believe after watching Episode One, but this episode is even more incredible and jaw-dropping. All the stars get a chance to stretch their acting muscles and add some layers to their characters. Plus, we're treated to what is probably the most shocking cliffhanger ever to be seen in Doctor Who.
Episode 3: The Curse of the Black Spot
Fun but forgettable. A simplistic romp which adds little to the main story arc. It's not terrible, but it falls far short of the show's usual standard of quality (which admittedly was pushed very high by the premiere).
Episode 4: The Doctor's Wife
Definitely the best of this set of episodes. It's so surprising and incredible that I can't say much about it without spoiling the genius of its premise. You aren't a true Whovian unless you've seen this, and even if you're not an avid fan, I guarantee you'll love it.
Episode 5: The Rebel Flesh
An enjoyable return to traditional Who. Very creepy "monsters" (though I'm not sure the term actually applies here). Thought-provoking and engaging. Plus, some things introduced in this episode will become very, very important in the future...
Episode 6: The Almost People
Even better than Part 1 (a rarity in two-part stories). Provides a satisfying, unpredictable conclusion to one of the thorniest ethical dilemmas the Doctor has yet encountered. Some of the FX are a bit over-ambitious, but that doesn't detract from the fun. And finally, we get some more plot development on the main story arc, in the form of yet another gasp-inducing cliffhanger. You really, really won't see this one coming, and you won't be able to keep yourself from watching the next episode.
Episode 7: A Good Man Goes to War
How should I put this? It's a mixed bag. The first half of the episode feels a bit like a rerun of Journey's End, and there are a few irritating bits and pieces randomly thrown in. Then the Doctor makes a mind-blowing discovery, and the second half changes everything for him and his companions - perhaps permanently. And we finally find out who the mysterious River Song is. If you've been watching very carefully thus far, and if you're the kind of person who sees the solution to mystery novels before you finish them, you may not find the revelation surprising. However, it's no less fascinating, and there will be parts of it you won't have been able to guess beforehand. In addition, we really don't find out everything about her in this episode. It'll be a long, long wait until autumn...
So overall, this first half of Series 6 gets five stars from me. We finally get some real, honest-to-goodness shocks and surprises, and all the main characters are far better developed than they were last year. Order today and enjoy.