zeborah

(Note that most of these complaints go for the stupid voiceover in part 1 of "The End of Time" too.)

they're pretentious and make you sound like a git.
They drain all narrative tension from a story. You think you're getting me worried about something and increasing tension, but actually you're giving me a spoiler about your own story. I could have spent that whole episode thinking "Will they all get out alive? They might all live, that'd be cool! Whee, they're escaping! --Oh crap." It would have been awesome.

[Well, okay, the villain killing the sidekick with her dying finger-twitch would still have been a tired old cliche. But if you're going to employ a tired old cliche, at least make it a surprise instead of an inevitability.]
Putting a voiceover in the middle of a two-parter and not at the start of the two-parter is structurally stupid. It makes it sound like an afterthought intended solely to make me worried etc. (Mutatis mutandis for "The End of Time".)
Related to 3), putting a voiceover from the point of view of someone who doesn't have the point of view of the actual story just breaks the, well, point of view.
How the flaming hell does Head Honcho Dinosaur Man know how much the Doctor's lost when Rory never existed?

I just. Actually I don't even know why I bother ranting about this when there were so many other reasons why that two-parter was total crap.

(If anyone wants to know how you do make a voiceover work, see Criminal Minds. --It's not a voiceover from the future, mind, which may be part of what helps. But this is what was awesome: for four seasons, every episode started and ending with a main character reciting a quote thematically related to the episode. Then in the last episode of season four they had a main character just talking, and that break in pattern was as unnerving as all hell.)