Maybe not necessarily "curves," but Shepard could have definitely done with more muscle. She had noodle arms in ME3. That's not what I'd expect to see in a soldier. to be fair, supposedly the Mass Effect verse has soldiers undergo mandatory genetic enhancement, not to mention Shepard's gotten a lot of cybernetics implanted by ME3. So, she's probably tougher than she looks.
I'd actually expect a more androgynous look in a soldier than how Shepard looks, though--especially while in armor. A soldier's generally in shape, so she probably isn't going to be huge-chested (Shepard isn't anyway), but she'll have bigger muscles in her torso and arms. Combine that with the bulk of her armor, and she should barely look different from a guy. She should move slightly different (no DA2 butt wagging, she isn't a puppy with a docked tail), and of course her face, hair, etc. should indicate she's a lady. But since this is a game, of course everyone wants it to be clear, if they pick a female character, that she's female--through more means than just her voice actor.
Posters above are right--everyone's body is different. But, Female Shepard never looked like any sort of athlete to me--the other poster who said she looks like the fashion model/actress body type that the media is pushing right now has hit the nail on the head, I think.
I'd just be happy if she didn't have noodle arms. The rest could stay the same. Not every woman has super-wide hips and I'd rather not every female in-game be Tali's body double.