The thing I like is that a pacifist playthrough is entirely possible, and maddeningly challenging. I havn't suceeded at it just yet, but it is doable. You get points for each kill only, and stars are for how many hostages you rescued. The trick is to end each level with a score of zero and 3 stars and with an overall score of zero.
I don't know if the game actually rewards you for this conduct or not, but it is EXTREMELY challenging.
The hardest part is that you need to path your way through the levels using grenades, ropes, and occasionally flash grenades in order to position yourself such that the hostages will be "safe" (defined as walking slightly farther than just offscreen) without getting them killed by the grenade throwers.
Doing level 1 like this is totally possible and doable, but the difficulty ramps up to 11 on level 2 due to the grenade throwers and the horrific positioning of hostages near them.
If anyone gets to the end of a pacifist run, let NG know!