I have a long history with smartphones, from the venerable Treo 180 all the way up to last year's winner, the Sensation. Quite frankly, the Sensation was a sensation. I'd have to spend way longer than we have today to find things with which I was not happy. It was snappy as hell and did the job, which, for me, has a lot to do with making phone calls.
Unfortunately I am burdened with T-Mobile through work, therefore I have dropped calls and bad coverage. This is not a fault of the phone, though. Since the contract on the Sensation was up, everyone was getting new phones at work. Being T-Mobile, the selection was limited and laughable.
T-Mobile has a reputation of being way behind the times with their offerings. The only standout candidate was the HTC One, therefore it was the only choice. T-Mobile doesn't really care what phones you want: you get what they offer, which isn't a lot, especially on the high end.
The reviews were largely positive, as checked at androidforums [they were just hacked - change your password!]. I even located a few people who had migrated from the Sensation and were happy.
The One is physically larger than the Sensation but much lighter. I like larger but don't care about weight. The screen is bright and sharp - it's a winner. As snappy as the Sensation was, the One is faster. Faster never hurts. The speed improvement is actually more marked than the last desktop upgrade I did.
I purchased a nice case with belt clip and kickstand so I'm off to the races. The wife agrees about the screen. I installed Angry Birds for my nephews and Yahtzee for her, so time will tell.
I read good things about the battery, which lasted over two days on a full charge. My total battery time will vary from yours, probably a lot, because I do quite a bit of optimizing to the system. Android Ice Cream Sandwich allows you to go into APPLICATIONS and turn off most programs, especially the annoying crapware that comes with all phones. It was a real joy to spend a few minutes making sure Faceyspaces, Twitter, HTC apps and Google Movies don't start up. Email is manual only. No live wallpaper, GPS, location or much else runs, saving quite a bit of battery for what I want my phone to be doing. A few days back I posted something on the steps I take to save battery life and be a bit more private in my phone use - it's worth reading.
WHEN DUMPING YOUR OLD PHONE
Yeah, yeah, lefty - you're a security and privacy geek. Why does any of this matter?
Because you don't want any identifiable information left on your phone when you give it back or away.
First make a backup, if you haven't already. This is very important for your data, not to mention transferring it to your new phone. Your phone has the option to back up programs to Google (I believe this is the default but please check for yourself). What this means is that if you allow it, when you get your new phone, it will automatically install the same apps (from Play) that you had on the old one. It will not restore the data.
Again, it will not restore the data. This is up to you. It will not restore any of the data, programs not installed through Play, music, or contacts not synched through Google already.
Since I am not Google's biggest fan (to be polite), I backed everything up to a computer or two. Android Assistant allows one to back up all apps, which can be imported/reinstalled on the new phone (or just go back to Play and reinstall them). The wonderful linux command rsync will sync the backup with the new phone and POOF, you're off. Windows users can COPY and PASTE.
The absolute last thing you need to do is restore your old phone back to factory new (and wipe the SD card, if applicable). Buried deep within the menus is a command to do this. Since all phones are different, there are no generic instructions I can provide (Google is your friend). There will also be a way to restore the phone to factory via rebooting and a key combination (Sensation uses VOLUME DOWN and POWER). Make sure you delete (or better, wipe) the internal card(s) to completely remove all of your data. Undeleting is easy, so keep that in mind. You want to return the phone in factory state so that nothing of yours remains.
Since it's a little larger, it seems to sit funny on its clip but this isn't a deal breaker. It's definitely louder than the Sensation, but the Sensation's audio sucked. There is some audio enhancement available on the One but it only works with the internal player (not interested, thanks). I suggest finding a nice media player and avoiding the Google ones (Google Phone Home). I'm waiting for VLC (now in beta) to get finished, as that's what I use on all my computers, regardless of operating system.
No complaints about phone calls or clarity from anyone and it sounds fine on my end. Haven't had a chance to check it out in the sunlight yet, as I don't get out too often :) Sunlight is the enemy of all displays so far (not to mention my eyes in the morning).
I used to save battery life by dumping the stock HTC launcher (and Sense) and going with a light launcher, like Zeam. Thus far, I'm not sure Zeam works properly with the One. It tends to make screen real estate smaller by putting an option bar at the bottom.
There's a cool `app' called No Wallpaper, which you can use to make your background black. This works perfectly for me and doesn't eat battery life like live wallpaper. It also enhances the display.
My only serious complaint at this point is that HTC(?) decided to get rid of the MENU key. It seems a complete waste of space when it appears on the screen. Either I'm missing something or this is really dunderheaded.
Also of questionable value are the decisions to make the battery non user replaceable and the internal card the only card. The card shares space with the operating system, leaving about ten gigs of usable space, period. There is no facility for another or external card.
I'm looking forward to more use of this phone and will provide details as I come across them. So far it's a winner.