I find my 5X annoyingly laggy, although only intermittently so. Also, the camera is pretty bad.
The longer version is that I'm probably somewhere around a 6 on a scale of 1-10 about the phone. It's a great value, but it's nowhere near the value my Nexus 5 was when I got it. That phone performed wonderfully with the only flaws being a somewhat weak battery and a terrible camera. The new phone retains those issues, but doesn't achieve the same level of performance (the already mentioned lag issues). The fingerprint sensor is nice and well-placed. The size is good, I'd hate to go any bigger and think I would prefer ever so slightly smaller. The screen is great. Voice quality is good. Basically, it does everything a phone should, but sometimes randomly decides to do it all really slowly for no apparent reason. It's a good deal because it's cheap, but unlike the Nexus 5, which performed as well as much more expensive phones in everything except photography when it was released, the 5X is noticeably inferior to the premium phones on the market.