First off, I had a Lumia 1520 and just got the 950XL, and I think the 950XL is a GREAT phone. It's fast, the camera is great, the touch sensitivity is phenomenal, and the build of the phone itself is (in my opinion) quite premium. Now, it's not metal like an iPhone, however, I find iPhones slick to hold and a little heavy. Aside from that, metal doesn't necessarily equal premium.
Having said all of the above, I will admit that for the first day or two, I wasn't sure about whether I'd made a good decision. I found that the battery drained a little quick, and the Windows Hello iris scanner worked intermittently (whenever I would click the unlock button, the scanner would either not come on, or it would immediately say 'can't recognize you'). So, after doing a little digging I found that people in several places (here included) mentioned that they reset their phones, then restored from a backup and it seemed to fix the issues they were having. I did the same, and I am here to tell you, it made a WORLD of difference. Now, EVERY time I click the unlock button, the scanner works perfectly. My battery lasts a LONG time (as in, I'm a fairly heavy user - mostly text, internet and email - and my phone goes from 100% at 5am to 21% at 11:30pm), and the quirks I was experiencing at first have ceased.
Basically, if you've got a 950XL, don't give up on it. It's a great phone, and Windows 10 Mobile is getting better all the time. The app gap WILL close eventually, maybe not all the way, but enough that I think we'll start seeing much greater adoption down the road. It seems to me that people forget that BlackBerry was once the king, and look where they're at now. Android wasn't so hotly received at first either, but it is now a powerhouse. The point I'm trying to make here is that Windows was a late entrant into the mobile game, but where Microsoft is different from everyone else is that they listen to their users and change the systems (PC, Mobile) to fit us. While most people point to Win8/8.1 and chuckle about how much of a misstep it was, the important thing to take away is that Microsoft went back to the board and made MASSIVE (probably costly) changes in response. So give it time people, it's all going to come together.