I promised a review of this device when I got my hands on one, so here goes.
I picked up the One on AT&T yesterday. I haven't really used an HTC device in quite awhile, and I'm pretty happy with this phone.
The very first thing I did was to unlock the bootloader. HTC (like everyone) got this very wrong in the past, but they finally got it right. The production device is fully unlockable on the AP side using an unlock code from HTCDev. It only took a couple of minutes to follow the prompts on the site and I was greeted with the UNLOCKED message in HBOOT. Installed CWM and did a backup.
This hardware is sexy. It's got clean lines and feels very solid when you are holding it. The 1080p display is gorgeous and bright, although I'm not convinced that I would pay a lot of extra money for 1080p on a phone if all other things were high-end. Oddly enough, the phone looks like the little brother of my Samsung Series 7 laptop which is a good thing. There are only two capacitive buttons, which took a bit of getting used to- you have to double-tap the home key to see the recent apps list. It's a good design, and it makes plenty of room for the front-facing stereo speakers.
HTC has taken a very different approach to software than Samsung has, and has chosen to focus on media and content instead of UX features. You're immediately greeted with the Sense launcher which has a full-screen pane that aggregates data from various social networks and news feeds. It works well and I find myself actually using it. There's so much room for improvement and additional data sources, but it's a good start. The launcher in general is pretty decent, at least until you open the app drawer. HTC has decided to go with a 3-column app drawer with a vertical tray that doesn't do free scrolling. It's very painful to use if you have a lot of apps. Folders are supported in the drawer which makes it a little easier, but it's still not the best experience. One feature that HTC did well is the lock screen. It supports a number of different layouts (I use "productivity") and shows you quick information without having to unlock the device.
The performance of the device in general is off the charts. Under the hood, it has the same chipset as the Galaxy S4, so the performance of both devices is similar. It's probably more horsepower than most people will need for quite some time.
Overall, I like where HTC is going with this. They have decided to skip the "kitchen sink" approach to really focus on a few things, and it works. It's also developer friendly, which is important to me and probably to most people reading this. I really think HTC might be back in the game with the One. It's an awesome device. They will of course have to contend with Samsung's unstoppable marketing machine though.
If I had to make the choice between the One vs the S4, my head would probably explode so I'll just carry both I think :)