I am a proud owner of the HTC One and absolutely love the device. I've owned a few HTC devices in my life (Apache 6700, Hero, Touch Pro, Evo 3D, and now the One) and have never been disappointed. Excellent build quality and a sleek look.
I also own an HTC One; my first Android device was the HTC G2, another unique and well-built Android device that was under-appreciated by the market (it had a pure AOSP build, even!).
But these devices are not the reasons why HTC is failing. For too long, they have been pushing crap device after crap device onto the market in search of low-end customers. The MyTouch 3G, the Droid DNA, the One V, and now the First are examples of this failed strategy; and there are countless others.
Samsung can get away with its low-end offerings because it has one flagship that it throws all of its marketing weight behind. HTC has only recently begun this strategy with the One, but I fear that this decision has come too late.
HTC should be doing what Apple and Samsung do: one flagship device per year, with the largest marketing budget you can afford. Samsung won mindshare by portraying itself as Apple's underdog; now that Samsung is huge, HTC has the same opportunity. And its industrial design prowess is an advantage that Samsung does not have.