I've seen people go back and forth on it but I've definitely gotten better battery life out of it and it seems a good bit smoother and snappier to me. I guess it depends on what's being done with it but I swapped back for about 6-8 hours last night to try my favorite 4.2.2 go to ROM and I didn't get the same bang out of my battery.
Just my feeling on it of course, but if I'm getting better battery on stock 4.3 than I did on a custom ROM/custom kernel 4.2.2, seems like it could really be a great update. Admittedly the improvements are under-the-hood but they seemed to really add torque and life to my nexus' engine. Faux's 4.3 kernel has helped a small bit as well even though I haven't tweaked his settings much yet, nice to have some color control already.
I'm also getting better reception (even if only slightly and partially placebo) with the .84 radio. The update has been good to me.
I'm extremely impressed with my experience with it so far, absolutely LOVE 4.3. Can't wait until the ROM's come pouring in and tweak it that much further. This device has some amazing devs.