I found face unlock to kind of suck also, doesn't work in the dark, didn't seem particularly accurate or fast, and my phone would forget my face every so often, causing me to have to delete and reset my profile. Iris scanning was a pita, the phone had to be held fairly close and at the right angle. Neither of those methods were very useful if the phone was lying on my desk, or if it was propped up in my car cradle.
Battery seemed a bit weak to me as well, but it may have been a combination of me playing with the phone more and also enjoying how bright it got. I actually found myself using it outside, where with the iPhone I don't as much because it gets washed out so badly in sunlight.
No lag, if anything I was VERY impressed with how lightning fast the UI was. This was easily the smoothest phone I've ever used, very noticeable. But in the end I returned it and went back to my 7+ and will try for the X when it's released.