HTC are good at the software side, but they've always been a bit shit at the hardware.
My smartphone life started with the HTC Hero, then the Sensation, then the One (M7). But after sticking with the One for so long, I needed to upgrade, and there just wasn't anything that felt worth upgrading to. So I eventually abandoned ship and got a Nexus 6P. And I love it!
I've always loved the SenseUI, and some of the HTC apps are great. I do miss some of it - particularly the contact merging and social media integration. But I can't see them ever tempting me back unless they really pull something out of the bag.
HTC are such a frustrating company, as, in *some* ways, they *are* 'quietly brilliant'. But in others, they're bloody useless. Their flagship phones never stay flagship for long at all, and until the One series, they'd be dropped, forgotten and left without updates well before a contract cycle was up.
With hardware specs, there's always an critically underpowered bit, such as the GPU or memory or storage, so that it undermines everything else.
They also have a habit of flooding the market with mid and low range models with way too many revisions that barely differ from each other, yet you get the feeling that they actually put a lot of development into them, and miss the mark every time. Whereas, at their peak, Apple made it look easy and got great results, HTC make it look like really hard work and get results that weren't worth the effort.
They remind me of the second incarnation of Atari. I had an ST(e) back in the day, and I loved it, but despite some clever bits, it was flawed and just not as good as the Amiga. Then came the Mega ST, the Falcon, the Lynx, the Jaguar... all had the potential to be brilliant, but all ruined by flaws and weird business decisions.