When Series 4 first aired back in 2008 I was a bit meh about this episode, I really didn't like it and thought it was a bit rubbish, mainly cos I had no idea what was going on. I thought the Vashta Nerada were a bit silly, if effective, and didn't really get who River was (I dont simply mean I didn't know who she actually is (we didn't find that out until series 6), I didnt get what she was meant to be, what the concept behind her character was i.e. that she's a future companion). Now however, I LOVE IT!!!
Of course it's not simply a story that's grown on me, like others. Due to Steven Moffatt's excellent writing and the nature of the Doctor/River relationship, this story has become so much more powerful after series 5+6 and I really think that the character of River Song and her story arc is a work of genius. Here she is, with David Tennant's Doctor, yet everything that happened with Matt Smith is in the past. Her death's so tragic, the Doctor being unable to tell her. And as for how Moffatt's linked this to the rest of the series, just amazing. YOu have hers and the Doctors little catchphrases ("spoilers" "I hate you sometimes!"), you have the references to future adventures ("I've seen whole armies turn and run away," not sure if thats a reference to the Pandorica Opens and/or AGMGTW. And how brilliant was the crash of the Byzantium in the end? EPIC!) and you have stuff in later episodes e.g the Doctor echoes River's dying words when he dies in Wedding of River Song, and, far more effectively, when River talks about how she'll one day meet a Doctor who doesent know her in the Impossible Astronaut, which is just heartbreaking when we know this is the worst day of her life and that it really does kill her. It's just epic, but on a personal level, and somehow is more epic than thousands of Daleks and explosions.
This episode is deeply moving and so, so sad, especially when having seen later episodes with Matt Smith. It's almost as good even without this though, the realisation of the virtual world and the little girl/cal is so sad+genius from the Moff, while it now seems obvious woth her seeing what the camera sees at the beginning I'd never have guessed how the 21st century girl was linked to the Library with Doctor and Donna. I dont think I've mentioned Catherine Tate and really should. I always found Donna a bit annoying but she gives a brilliant performance here, her "marriage" and the loss of her family being just as heartbreaking as the Doctor/River relationship. Other standout performances are those by the actors playing Dr Moon, Miss Evangelista and especially the guy playing the Lux bloke whose a really great character and see's a lot of genuine character development. I dunno, there's something about him that steals the show, I cant think where I've seen him before. Is he in Psychoville?
But yeah, a real cracker of a story that is a great standalone of the Tennant era as well as serving as both a lead up and a conclusion to the characters, relationships & dynamics of the Smith era.

Of course it's not simply a story that's grown on me, like others. Due to Steven Moffatt's excellent writing and the nature of the Doctor/River relationship, this story has become so much more powerful after series 5+6 and I really think that the character of River Song and her story arc is a work of genius. Here she is, with David Tennant's Doctor, yet everything that happened with Matt Smith is in the past. Her death's so tragic, the Doctor being unable to tell her. And as for how Moffatt's linked this to the rest of the series, just amazing. YOu have hers and the Doctors little catchphrases ("spoilers" "I hate you sometimes!"), you have the references to future adventures ("I've seen whole armies turn and run away," not sure if thats a reference to the Pandorica Opens and/or AGMGTW. And how brilliant was the crash of the Byzantium in the end? EPIC!) and you have stuff in later episodes e.g the Doctor echoes River's dying words when he dies in Wedding of River Song, and, far more effectively, when River talks about how she'll one day meet a Doctor who doesent know her in the Impossible Astronaut, which is just heartbreaking when we know this is the worst day of her life and that it really does kill her. It's just epic, but on a personal level, and somehow is more epic than thousands of Daleks and explosions.
This episode is deeply moving and so, so sad, especially when having seen later episodes with Matt Smith. It's almost as good even without this though, the realisation of the virtual world and the little girl/cal is so sad+genius from the Moff, while it now seems obvious woth her seeing what the camera sees at the beginning I'd never have guessed how the 21st century girl was linked to the Library with Doctor and Donna. I dont think I've mentioned Catherine Tate and really should. I always found Donna a bit annoying but she gives a brilliant performance here, her "marriage" and the loss of her family being just as heartbreaking as the Doctor/River relationship. Other standout performances are those by the actors playing Dr Moon, Miss Evangelista and especially the guy playing the Lux bloke whose a really great character and see's a lot of genuine character development. I dunno, there's something about him that steals the show, I cant think where I've seen him before. Is he in Psychoville?
But yeah, a real cracker of a story that is a great standalone of the Tennant era as well as serving as both a lead up and a conclusion to the characters, relationships & dynamics of the Smith era.
An estuary of sorts, the Doctor's tide that goes in and goes out again while sitting on the dock of a bay.
Definitely some of the best episodes of Series 4!