It shortens some distracting side-plots (such as a woman who, bitten, develops unfortunate symptoms). Let Me In also tries to keep the dreariness, desolateness of the Swedish film intact but it does so without duplicating shot for shot. Whereas the first film’s jungle gym is all blank, snowed-in whiteness, in this film it has the sickly pallor of an off white streetlight.
Another part of this film which is striking is the marginalization of the mother. You never see her face. She is passed out, back to the camera or out of frame in every shot. It is a very cinematic way of letting you know she doesn't matter.
There are also explanations in this movie—more so than in its Swedish sibling—but these are told with looks and old pictures rather than in any dialog. The character reiterates that she is not a girl more in this film. You can interpret this in different ways depending on if you have read the book or not.
One thing I always ask about any remake is; why remake it aside from money? I know money is what matters and that no foreign film, especially a horror/suspense film, is going to do the numbers you get when that same film has actors who speak American. In an ideal world you only remake if you are going to add something to a film and this one does and it does it in very subtle ways. I feared it might be ham fisted and cheap but it isn’t that at all.
It is shot very well, as suggested above. It has a dark feel but you can still see everything, I do not know how a camera person and cinematographer team up to do this but they can be proud of this film. Usually when you say something "is dark" you just mean you cannot SEE anything.
And where are all these good kid actors coming from? First Case 39 then this film. Even the bit parts are solid actors, a bully who conveys both rottenness and empathy, a stoic boy with no friends who is stone faced but who melts in a scene by himself, talking on the phone.
If you are going to remake a recent movie, please be sure to do it at least this well ok?