I'm still using the iPhone 7 Plus, personally waiting on the iPhone X Plus version as I really like having the huge screen area. Having said that, I have set up a few iPhone Xs for friends and family and I can tell you a couple points that are my OPINION.
1. It's a "new" iPhone. Everything from the 6 through the 8 are basically the same phone, just more refined in a few cases. It's almost as if you were to buy a car. Imagine let's say a.. Toyota Camry. A 2016 Camry is going to be better than the 2015, but it's ultimately the same car. However, if you jump to the 2018, it's pretty much an entirely new car.
2. Using it is surprisingly intuitive. Even though I only used the X to set it up, I actually found the new gestures easier to use and just plain better than the older iPhones. FaceID adds to the intuitive nature of the phone.
Otherwise, I think it's pretty much a wash to be honest. Why pay the extra money? The way I see it, the bump over the 8 is justified because I'm getting a new phone. I think that's an easier to sell than paying more for an 8 over a 7. Having said that, I would never buy an older version, heck I don't let any friends or family buy an iPhone after the new year, as I believe it's better to wait until the new version comes out. However, in the limited scope of 7vs8 and 8vsX, I think the price jump for the latter makes more sense. The X is the future, definitely.
Most people are going to simply defend their own purchase, as such, keep in mind their biases. Since it is the middle of February, I personally think you should hold out till September unless you really need a new phone. But that's just me. Good luck!