People have recently been asking me this very question. So I'm going to answer it.
I think it was asked partly in jest and partly out of genuine curiosity. At the time I couldn't really give much of an answer; I'm not very good on the spot like that. All I could muster was an "I like it, I'm happy with it."
But I've since sat down and thought about it. I've only had the Lumia 950 Xl for a couple of months, and it's mine, bought with my own money. And some would say I has gone mad.
I'll be honest in that I am a little surprised myself, given that I had a Lumia 950 around launch time from Microsoft and I didn't have a great time with it. But Windows 10 Mobile is a lot better now than when these phones launched.
So, here's what I've narrowed down to so far.
A large screen without being massive
I used a Lumia 1520 for a while. I even remember the look on a gentleman's face as I gave it to him with my boarding card on before boarding a plane to Spain a couple of years ago. It was just too big. Not even just because I have small hands — it was just a giant of a thing. I also wasn't ever too keen on the squared-off corners, especially on something that large.
The Lumia 950 XL is a good balance of size in both regards. The display is plenty large enough for my own purposes, but the body isn't unnecessarily gargantuan. It still fits in any pocket comfortably, and I don't feel like I'm holding a table to my face to take a phone call.
On paper the differences seemed small, but when it comes to something you're holding as often as your phone, those small differences are soon magnified. The display in the 950 XL is also higher resolution than that on the old 1520, and it's a glorious thing to look at every day.
Great camera and a physical shutter button
Lumia owners are spoiled when it comes to having a physical shutter button on their phones. Sony offers the same over in the Android space but it's not common at all. It's one of those things that you might never realize you miss until it's gone.
Lumia phones have had good cameras for some time, with even the likes of the 640 XL defying their price tag when it comes to shooting pictures. But the camera on the 950 phones is really good. Or I think it is, anyway. It might not be the outright best smartphone camera, but it's not disappointed me yet.
The only thing I miss is panorama shots. Please, Microsoft, just sort that out, OK? I can't install Lumia Panorama on this phone and the third-party apps that are available are pretty poor on Windows 10 Mobile.
The battery is big and removable
The designer quest for increasingly thin smartphones always takes its biggest toll on the battery. The engineers can squeeze in more capacious cells and the developers can optimize the OS until the end of time, but in the end, physics always wins. Add to that my heavy use of the phone — between Netflix and streaming music and podcasts and taking photos of my kid and games and email and so on, there's just a lot hitting my phone's battery hard.
The battery in the Lumia 950 XL is both large and removable, which suits me down to the ground. Quick Charge is fantastic, too, especially with a compatible portable battery pack. But I like that I can probably last most of even a heavy, heavy day, but just pop a fresh battery in should I run out.
This one's still developing, but the more I try Continuum the more I like it. I use it with the TVs in my house when I want a bigger screen or to do a little work when I'm away from my desk. I've got an Amazon Fire TV Stick which actually works OK wire-free, and a cheap USB-C hub that allows me to wire in and charge my phone at the same time.
I work from home and I don't spend all day in the same room. In the mornings I'm hopeless before breakfast and a couple of coffees, but just plugging in my phone and catching up on a bunch of things before I start the day is fast becoming a favorite routine of mine. I could take a laptop upstairs, but I already have my phone there charging, so it makes more sense to me.
The hardware on the 950 XL hasn't yet felt sluggish when using it through Continuum, which is perhaps the thing I'm happiest about in this situation.
I actually like Windows 10 Mobile
This is the one where fans of other operating systems will collectively sit with a wide open mouth or something to that effect. Readers of this site shouldn't be too surprised, of course, but I do think it gets a lot of flack where it isn't necessarily warranted. Yes, it's far from perfect. But Windows Phone 8.1 wasn't perfect. Android isn't perfect, and neither is iOS. I like the user interface, much more so on larger displays than its predecessor, and new apps built for Windows 10 are a great improvement over older versions.
Microsoft offers a good mobile experience on all platforms, but since I'm invested in its services anyway, I still think the overall experience is better on Windows 10. Outlook has given me sync issues on Android, the Groove apps really are sub-par elsewhere and I love the new Xbox app (which you can't get on Android or iOS). Live Tiles are also much better than widgets, and don't ever try to convince me otherwise.
There's also the so-called 'app-gap.' Maybe it's because I don't care at all about Snapchat or Clash of Clans, but I don't feel it. There is literally one app which I really miss having on a phone, and that's Authy. It's a cross-platform two-factor authentication code generator which I can at least access on my desktop (even if it means Google Chrome is installed for that one reason), but it's the best app I've ever used for this purpose. It hooks into everything — Twitch, Microsoft, Dropbox, Google, and so on.
There's still work to be done, but that's fine. There's always work being done on Android and iOS too. I'm particularly looking forward to Messaging Everywhere rolling out to the public. I already love being able to see missed call notifications through Cortana on my PC, I can't wait to be able to do the same with messages.
I could probably go on a little further, but those are five of the big things that currently having me use a Lumia 950 XL and like it. I wish the Camera app wouldn't trigger a reboot of the whole phone at least three or four times a week, but bugs can be fixed. I'm fortunate enough to have many phones slide across my desk, but only this one is actually mine right now.
If you're a similarly happy owner, be sure to share your own experiences in the comments below. Likewise if you're not, we don't judge!