Actually, I'm going back and reading the parts I skipped the first time around. I've been working my way through the whole Twilight series, and by the time I got to this very thick book that ends it (had to wait about 3 months on the library holds list), I wanted to cut to the chase and find out a) what kind of payoff she'd cooked up for the sexual tension around which the first three books were largely built, and b) whether the childbirth scene was really as gothically horrifying as everyone said.
It's hard to speak critically about the Twilight books. If they work for you, then you're willing (I think) to let a lot of technical/craft things slide, and if they don't work for you, then chances are they fail on such a fundamental level that there's not much point in discussing the mechanics. I admit I fall into the latter group. These aren't books I would ever re-read, or recommend to any teenage girl.
But I have to say I'm baffled as to why so many readers who gobbled up the first three installments were so affronted by Breaking Dawn (to the point of returning books to the store, etc.). I actually saw a lot of improvement in her prose - the dialogue tags weren't nearly as obtrusive as in the first book - and while, for example, the plot is nonexistent in places and preposterous in others, wasn't that true of Eclipse and New Moon as well?
Anyway, as to the sex, I think she painted herself into a corner. Having made the decision that she wasn't going to write explicit scenes, but having made it so prominent a concern of Bella's and Edward's, she was forced to address it by having the characters talk and think about how amazing it was without letting us see/judge for ourselves, which, aside from whether readers who'd been looking forward to that part felt cheated, made it a massive writerly instance of Telling instead of Showing.
The childbirth scene... well, I tried to read it but as I was skimming at that point and hadn't figured out that it was being told from Jacob's POV, I had a hard time getting a handle on what exactly was going on. Anyway, yeah, it looked pretty gruesome, but I don't necessarily mind that. Jennifer Donnelly, in A Northern Light (YA with an early-20th-century setting), writes a vivid account of a rural birth with no drugs or proper sanitation, and I think it's my favorite, most true-ringing account of childbirth in fiction.
For better/worse, I'm nearly up to the childbirth scene again. Just got to slog through this last bit in which the werewolf pack are reading each others' minds with all their dialogue written in italics, and then I can give it a closer look.