I will begin by saying that I switched to Android from iOS with the HTC One M7. I loved that device, and with a few exceptions, the M8 delivers the same experience and improves upon it. What makes the HTC One such a great device is the physical design - what features or bells and whistles it might lack are made up for with a durable, efficient and beautiful build.
The HTC One is a great device for anyone due to its ideal size - the screen is large enough that it is fine for all but the most-demanding games, but it uses most of the face of the device so it is not too large and cumbersome. The switch to on-screen function keys helps this. It might be a small thing, but the symmetrical face of the device makes it good for switching between vertical and horizontal orientation. The speakers are equally placed on either side of the screen so that when viewing content in horizontal orientaion the speakers project to your ears with balance. The one complaint I would make about the screen is that although it's larger and still 1080p, the pixels are larger and lacks the crispness that the M7 possesed.
The speakers, being placed on the top and bottom in horizontal view, are great. They are flat to the device yet leave nothing to be desired. I did not appreciate the stereo effect until later using Samsung devices with a single speaker, offset to one side and facing away from you. As mentioned before, the HTC One is designed so that the speakers project towards the viewer, creating the experience neccessary to fully enjoy HD video or Android gaming.
The device is well designed around the edges as well - The volume buttons are on the side and are destinct enough that I never increased or decreased volume accidentally. The power button is on the top-right and flush to the decive. The M7 had a flat button as well, which I like since it makes locking/unlocking the device intentional. I especially like that the M8 button was switched to the right side - pulling my phone out of my right-hand pocket made for unlocking to check time and notifications quick and easy. I didn't appreciate it at first, but putting the headphone jack on the bottom of the device was a good choice as it results in the headphone cord falling downwards naturally when holding the device verticlly. The headphone jack is a bit close to the corner, which makes it somewhat uncomfortable using with two hands horizontally, such as in gaming. Finally, the addition of a Micro SD card slot fulfilled another feature that is important for users that store a lot of content. The card is placed into a little tray that ejects by using a pen or pin, so the Mircro SD card becomes part of the device.
The software/interface contains both positives and negatives for the HTC One experience. For one, the recents tab is rather straightforward. The recents tab open to take up the entire screen, displaying tabs in a 3x3 grid and generating previews of the content. The most recent apps are in the bottom-left and move to the top right as they are replaced. The recents also has a close all button, which I expect in a device but is still up to the manufacturer. The settings and control over the device are fine, especially with the small details such as displaying the battery percent and being able to change the device's font. The bad part of the HTC software/interface experience is that the stock apps are mediocre at best. The camera, clock, calculator, etc. get the job done but are not particularly great. HTC frustrted me some by being overanxious to try out new stock apps that I'd rather do without. The "Scribbles" notepad is strange and unwanted. The tasks and calendar are efficient but rather boring and uneventful. HTC is trying much too hard with their "Zoe" feature for creating photo and video collages to music. It appears that the upcoming features of downloadable and custom themes is also features I would prefer to delete for extra memory space. The HTC Sense homescreen is fine except the insistance for you to use the news/social network tab. I never looked back once switching to Nova Launcher. Finally, the quick settings require an extra button to be tapped after dropping down the notifications. This might not sound like a big problem, but after using other phones with the setting built-in to the notification menu made me realize the lack of foresight on HTC's part.
The HTC One has plenty of power. I never had a problem with the device being able to run the apps and games I desired. Only the most demanding games would challenge the device. It will slow down after too many apps are running. This surprisingly became more of a problem with the upgrade to Lollipop. The apps seem to be kept running indefinately, whereas in Kit Kat I can only assume they would be forced to closed after too many new apps are opened. The HTC upgrade to Lollipop on the M8 seemed to age the device quicker than if it had remained running Kit Kat.
The camera is perhaps the biggest dissapointment of the M8. Despite sounding good on paper, the camera often lacked the ability to capture sharp and pleasing images. It seemed to do well at times, such as landscapes in daylight, but I always struggled to get anything decent inside or with the flash. The lack of a poweful camera seems to be a continuing problem for HTC devices.
Despite mediocre stock apps and a subpar camer, the HTC One M8 is a great smartphone due to its convenient design and well-rounded performance. The device is the perfect size for enjoying content but not making it difficult to reach places on the screen or fit into your pocket. Some will complain that the metal body makes the device easy to drop, but I always use a case and this elimates the problem. The subtle design and balanced features comes together to make it a great pocket companion.