I've had my one for about a month now. I wanted to be able to give a more honest review after the honeymoon period.
I love the phone.
As a phone, the sound quality is great, on both ends. I have yet to run into any issues with the antennas in the phone. I get signals and lose signals in the same places I did with my HTC rezound on Verizon, I switched to at&t specifically to get the One and find coverage is pretty much the same. It's difficult to know if the antennas are better or worse than previous phones due to the carrier switch but it seems to get a stronger WiFi signal than my rezound did. Over all, I would guess the aluminum body doesn't hurt the signal strength. I only mention this because of early fears the One would suffer signal issues.
I also read reviews that complained about slow GPS lock, I have not experienced this at all. It seems to lock just fine for me and do so quickly without any difficulty.
Texting is something we do probably more than anything else with our phones and the ones keyboard is awesome! I've used swype on all my previous android phones. I didn't bother installing it on the One. Its version is every bit as good, if not better. I also love the customized texting screen. Very cool to have options to significantly change the look without going with a third party app.
Every android phone I've ever owned had weak external speakers. Having to cup your hand behind it to barely make out sound in even modestly noisy environments. The HTC One is the first phone I'm actually having to turn down! I even use it as a bed side radio.
The design is beautiful but not without its faults. It is a slippery phone in hand. This has been fixed with the application of an Xtreme guard film. (Absolutely wonderful product and price BTW). The rounded back makes texting or typing difficult if the phone is sitting on a table, like at lunchtime at work...but it's a small quibble. I find the phone to be beautiful and very sleek looking. It feels very satisfying in the hand. The weight and coolness of the aluminum feels, well, like a real premium device. No other way to explain it.
If you're reading this you probably already know the screen is incredible. It has a wide viewing angle and is actually perfectly viewable in direct sunlight! This is the first phone I've owned that you could see clearly in direct sunlight.
The "ultra-pixel" camera, I'm still not quite convinced. The rezound took crisp beautiful photos, even when blown up. This camera takes some very nice photos but to my eye they just don't seem as well defined and crisp. I will need more time fiddling with it before I can say definitively that its not as good. The software however is really great. The Zoe feature is cooler than I thought, you can use it like a burst, selecting the best photo. You can also let the phone stitch zoes and stills together to create a very cool video clip.
Battery. From what I gathered on the net prior to buying the One was that I may not be able to make it past eight hours on charge. I'm happy to say, I get 12-14 hours easily on work days. If at home and I sit playing games, reading the net and watching YouTube, yea, I'll get like five or six hours out of it. At work, I would be swapping out my rezounds battery for a fresh one after four hours or so. The One gets me through my entire shift (12 hours) with 50-60% on average left. That's keeping the battery saver feature on of course. In use, I don't notice a slow down in performance using the battery saver but after running benchmarks with it off and on, it definitely slows it down. But like I said, I don't notice it with use playing games or watching video etc. So in my opinion, the battery is fantastic.
As far as performance goes, the phone is smooth and fast. Have yet to see any sort of lag. Obviously its top tier at this moment, so that's to be expected.
I'll be honest, I've always loved sense. I love the pretty matching widgets, the cool 3-d effect on older versions. Sense 5 seems stripped down. I don't care for the new widgets, the clock was a big disappointment to me. It's more like functional and simplified I guess. I thought I would also hate blink feed but I actually love it! I really enjoy the easy access to internet articles and the customization to tailor it to my taste. I still have it on the farthest page to the left but visit it often. Aesthetically I don't like the 4x4 layout. The power control widget doesn't look good stretched tall due to the 1x1 square being taller than it is wide. I wish I could change the layout on home screens. Not a deal breaker but it just bugs me.
Over all, I am very happy with the phone. It vanishes in my pocket and is easy to carry. It looks incredible (in stealth black) and performs perfectly. It's the first phone I've had strangers ask me "woah, what kind of phone is that?". Guess they must be living under a rock....or maybe just aren't as into cool gadgets.
I would highly recommend this phone to friends and family.