Note: Doze in Marshmallow will extend your overall battery life if you don't use your phone.
Good point, sorry, I was replying in a rush and didn't have time for more details. Indeed, Doze basically realizes every time your phone is on a table or simply laying down unattended, and turns off most sensors while restricting a lot of program functionality. This results in, for instance, your battery going down by only a couple percent points when you leave it on overnight while you sleep. My Life One X tends to go down about 10% overnight, so that's quite an improvement. If you keep your phone on the table during the day, you'll also feel the battery benefit. I believe in Android N or O they intend to make Doze even more powerful, recognizing when it's in your pocket to execute the same kinds of battery saving modes.
There's more benefits from M though, I can't recall everything - check Ars Technica's review of M - but I think I recall they did changes to how apps build themselves upon installation and the ART runtime so that now it should be much faster to install apps too. There's more stuff, but I can't recall.
1 day left! C'mon BLU!