I've been an iPhone X owner now for four (count them) whole days. I switched from a Galaxy S8 plus. Things I've noticed:
- Call quality is far better on the iPhone than on the Samsung. I thought my house was on the edge of coverage because I could only get decent reception in the kitchen and even then it would break up. Now I get crystal clear reception everywhere in my house. It's like they built a new cell tower on my street.
- The app I use most is Audible. On my Samsung it would appear to time out after about four hours, such that when I got in my car after a day at work it would not automatically start playing. I would have to get my phone out, unlock it, open the app, press play. Although the Samsung has more memory it appears that iOS handles audio threads much better.
- Audible on iOS has an 8 minute sleep timer (perfect!) whereas on Android the shortest is 15 minutes which is too long. Why the difference? Obviously this is neither Samsung nor Apple's problem but it affects my experience and that's what matters to me.
- I miss the headphone jack! Why did they remove it? Aaarrgghh!
- The S8 charged a lot faster than the iPhone. I've not had the iPhone long enough yet to determine whether the battery lasts as long under normal usage but I need to change my behaviour around charging. The charging speed was a big plus for the S8+.
- Unlocking is *much* faster on the iPhone. FaceID is much faster than Face Unlock (and more secure).
- Pausing/playing Audible is a lot easier. On the Samsung I had to double-tap the screen which sometimes woke the device but oftentimes didn't. Then I had to swipe the clock out of the way to get to the audio controls (not easy when you're in the shower). Then click play/pause. On the iPhone I do a light tap which always wakes it, and the audio controls are right there front and centre.
- The "soft" home button on the Samsung was temperamental - sometimes it worked, sometimes it just triggered whatever GUI content was under my finger. So to play safe I ended up having to swipe up from the bottom to get the controls, then press the home button. Now I just swipe up from the bottom.
- Sound quality through the onboard speakers is much better than the Samsung.
- There are apps I can finally use that I use day-to-day on my other devices (like Things 3 - I *love* having that on my phone now.)
- It still works with my Samsung Gear S3 watch! For the most part.
I never used my watch to reply to emails and so on so I've not lost any functionality I actually used. I think the Apple Watch is hideous and I'd rather strap a dog turd to my wrist. No offence, Apple. 
- I love the better integration of voicemail on the iPhone.
- Animojis are tons of fun! But I've never sent one to anybody and probably won't. Maybe I should have got an iPhone 8.
/edit - Ignore that last bit. I just sent one to somebody (who has an Android phone).
- Android was a better at handling global settings like font sizes. My eyesight is pretty crap these days so I have to crank the font size up. In most cases on the iPhone this is fine but things like the book list in Audible (tiny!), BBC news app etc. simply ignore the setting and go their own (too small to see) way. The Android ecosystem is more consistent across apps.
- iTunes still sucks. Hard.
Anyway, if you read all of that, thanks! Have an ice-cream or something.
TLDR; I'm glad I switched. For the most part the iPhone X experience is vastly superior to the Galaxy S8+ experience. There are a few annoying niggles.
/edit - no chance anyone reads this!

/edit2 - fixed a typo at the end where I said S9 instead of S8+ by mistake. Thanks for pointing it out.