Just picked one of these up to replace my HTC One M7 and initial impression coming out the box is just wow, the screen is amazing both size and colour reproduction wise. Coming from a 4.7" 1080p screen to 5.7" one you can tell a little difference in pixel density but doesn't detract from the experience at all. Battery life is great so far and s-pen, despite bad rep in the press is a very nice addition to some apps.
I do have big hands so feels great to handle but does feel somewhat tight in the jean pocket, just picked up a Spigen case which is also top notch quality but adds more bulk so will see how easy it is to live with in the coming weeks. Only area that feels little underwhelming is the camera which I suppose is from the S4 era so not the newest tech. There's a processing pause after every shot and doesn't appear as snappy (pun not intended) as M7 but definitely a lot more consistent, will have to see what it's like once I've had a chance to test it in different scenarios.
Also I wouldn't call it laggy but it isn't as smooth as the M7, no lollipop update on this one yet so see if that makes a difference.