I've been dutifully avoiding spoilers while trying my best to skim reviews just to get a feel for their thoughts and impressions and I've yet to come across anything that I think will severely disappoint me when I see the movie myself.
The RT % really means nothing to me. this is one of those kinds of movies where I really think that engaging with what the critics are actually saying is important (though, yes, hard to do completely when you're trying to stay spoiler-free). There are a couple outright pans but most of the "negative" or middling reviews have some very strong praise mixed in with what they perceive to be the movie's "flaws," and most of those flaws are present in just about every Nolan movie to date. i guess it's a good thing that i like Nolan movies.
obviously, i want Nolan to grow as an artist, too, but it really does sound like he has, both aesthetically and in terms of emotional storytelling (or at least he's trying to push himself in those areas). some are finding fault with the lack of grace in the exposition and some convoluted and/or unnecessary aspects, etc., but i wasn't expecting Nolan to grow out of those particular traits on this big-scale, ambitious sci-fi passion project.
you also read the reviews and get a strong impression that this is a film that's trying to say something. that's to be lauded. Gravity, for instance, was all about the experience and immersion and was technically virtuosic, its basic themes and storytelling rendered simply to serve that end, and so in that way it was virtually critic-proof. i enjoyed that effective experience very much in the theater, but at the end of the day it is not a movie i'm going to return to much at home, or spend much time thinking about or discussing. i'm not saying Interstellar will be that type of movie, but it sounds like it is, and i'm hoping.
maybe i will agree with some of the reviewers that have major issues with some of the choices that the film makes in what it tries to say or how it says it (but there is no consensus there, you read one review that lauds one part of the movie while slamming another while another review does the exact opposite; i'm seeing some very diverse reactions to the film's ending...heh, still while i'm trying not to find out what the ending is). to me, that's a good kind of polarizing, because obviously there is a film with some considerable merit to it--in terms of conceptual ambition and some technical aspects, if nothing else--but it is going to engage with viewers in very different ways and generate an interesting dialogue. and what's fun with that, too, is the huge array of opinions that will be brought to the table because everyone and their mother watches Nolan movies, as opposed to provocate smaller films that people get to see in NY and LA and then maybe the rest of us get to catch if we live in a big enough city.