Spectacular. Absolutely beautiful. Cinematically, this movie is one of the best ever made. Story wise - it both tells the story of a superhero and a crime-ridden city with corrupt people, a love triangle and a tragedy, the corruption of good ("you either die a hero or live long enough to see yourself become the villain"), but also the goodness of humanity that overrides even our desire for survival.
There's nothing about this movie not to like. The returning and new actors are incredible - Heath Ledger as the Joker will make you crazy, but just enough so you can keep watching. Aaron Eckhart as Harvey Dent will leave you wondering, and his character is developed just enough to make his arc perfect - to keep you wondering but not shocked.
Bottom line: whether you're into superheroes or not, DC Comics or Marvel, whether you've watched every Batman movie and read every comic or haven't seen a single one, this movie is well worth watching. You're probably better off watching Batman Begins first (that is incredible as well) but I don't think it's necessary. You'll just find some of the information new, which is always fantastic.
And BTW, no pressure to watch The Dark Knight Rises after this. It's not a bad film but it kind of disappoints. See my review here: https://www.amazon.com/review/R3TKBV8CSCXFOE/ref=cm_cr_srp_d_rdp_perm?ie=UTF8