Like locker_monster, I came into this episode with low expectations, because I saw Frank Cottrell Boyce's name in the opening credits. "In the Forest of the Night" is, to me, by far the worst episode in all of Doctor Who (okay, to be fair, I have not yet seen "Time-Flight"...), and it was very difficult to watch an episode by the same writer without prejudice. I think I did give it a fair shake, though, and I didn't find it to be bad. I just didn't find it to be good.
Simply put, it was boring. There was just too much talking, to explain everything to us rather than let the puzzle reveal itself. I actually started zoning out near the end. It was basically boring enough that I don't have much to say about it, except for two inconsistencies that bothered me and one thing I'm starting to get really sick of.
Inconsistencies: Maybe it's because I've been reading Brandon Sanderson books, but I am finding that when I'm watching a show, I'm trying to figure out how the system works: what its rules are, and how the hero is going to defeat it. It's a huge problem when reading Harry Potter, because that world's magic system is so poorly-defined, there are inconsistencies everywhere. For this episode, how exactly did the emoticons work? Did they reflect what you were thinking or what you were displaying? They could show when you had an idea, which is not an expression, but they'd smile when you were smiling, even if you weren't actually happy. Well, the whole system was stupid in the first place, but it would have been nice if it obeyed its own rules.
Second: Bill asks about the evacuation of Earth and if this is the last remnant of humans, and the Doctor says many ships were sent out and that he'd encountered a few before, and yet later, the Doctor is screaming about saving these people, because if he doesn't, then the human race would be extinct. Which is it, Doctor? (This feeds into another thing I'm sick of: every situation being the possible end of the world, the end of the universe, the extinction of the humans, etc. Not everything needs to be apocalyptic.)
And finally: What is with the mind-wipes? After an episode that made a big point of "You shouldn't mind-wipe people, Doctor", the Doctor mind-wipes an entire species? Or is the point of this episode "It's okay to mind-wipe sentients as long as they're not flesh sentients"? Of the last four episodes, three have ended in mind-wipes. You could say it's four mind-wipes in five, since "Heaven Sent"'s point was that the Time Lords were resetting the Doctor's experiences in the maze until they got what they wanted. Message to the show: Mind-wipes are cheesy plot devices. Stop it.