HTC One looks great. I like the industrial design. I could almost just buy it on looks alone. I like how HTC phones make substantial evolutions each year. Just having seen the official shots of the Galaxy S4, I was disappointed that they didn't try a new look. To the untrained eye, it could be confused for the S3 or the Note.
I'm impressed that they made the One out of metal. And the one thing that the HTC One addresses that has always bothered me about Android phones is speaker placement. Having the speaker on the back never made sense to me. HTC One gets a lot points for that.
I've always liked how Sense looks. It looks way better than Touchwiz or Blur or even AOSP. And with the HTC One's power, Sense can be good-looking AND fast.
The camera being physically only 4MP doesn't bother me. I'm glad that it can take good low light photos. That's another thing that has always bothered me about cellphone cameras, bad low light performance.
The only thing that I might have an issue with is battery life and the height and width of the phone since I have small hands.
I would usually gripe about not having an SD card slot, but I think 32GB or 64GB is enough for me and probably for most people.
The bad thing is, it's hard for me to imagine HTC making a comeback with this phone. I think it's a better phone overall compared to the S4 but if HTC doesn't market the One enough, they'll be in trouble.
I don't want HTC to go away, I've always appreciated their efforts to innovate.