I've been following the iPhone5-S4 threads for like a month now, but it wasn't until that CNN article "Android phone that could crush the iPhone" that I learned about the HTC One. Thread + major phone review sites sold me though.
My Impressions (like most people beforehand):
Display is nice, can't distinguish pixels (haven't seen S4)
Fast, snappy phone.
Good daylight camera
Great low-light camera
Sound is 1 of a kind.
Looks & feels of premium.
Battery life seems above average, wouldn't say Note II status. 100% to 40% after 8 hours low-moderate use. Power Saver On. Don't have phone on me so can't Screenshot
The only thing I can find to dislike, is that the phone gets warm when using it (jumping between apps in a short period + on LTE.) It doesn't get to burning temperature, so it's doable. Not using a case. Will be a great hand warmer in the winter.
I remember the first time I loaded up Youtube in the kitchen, my gf said it sounded like the TV was on in our kitchen 50ft to our living room. It's not overly loud, it's just clear and crisp.
Sense is not really a problem now to me. I'm coming from Stock Android & MIUI.
I sent back my first One since there was dust under the screen out of the box.
Another thing I miss is the quick settings when pulling down the notification bar. Fortunately, that's a main feature of 4.2 which I assume HTC will update and hopefully not botch.