Compared to my 7 I'm getting very impressive results. I'm not a heavy user in that I don't play a lot of games on it, I don't stream a huge amount of content either (IMO). Everyone's results and usage will vary, but for me, as a reference, I used to only just make it through the day (sometimes needing a top up towards the end of the day) and get between 5-7 hours of usage.
Obviously I have been using the iPhone X a lot more than I usually would because shiny, but Saturday and Sunday, when I was using the thing none-stop, it survived the day. Yesterday I got about 15 hours stand-by with 9 hours of usage and was on around 9% when I put it on charge for the night. I'll be interested to see todays results now that I'm at work and should return to somewhat normal usage for me.