I've had this phone for about a month now and I can say it's the best Android to date, but it sure isn't an iPhone killer.
What I loved:
-4G LTE speeds are amazing
-performance is great, 1.5Ghz processor really makes things smooth
-phone design is up there with iPhone design, I think HTC did an amazing job
-screen is up there with the quality of iPhone screen and it's almost Retina screen as well
-light weight, very thin (I originally though it would be awkward in the jean pocket, but I barely feel it)

What I didn't like at all:
-bloatware from AT&T and HTC just ruin the fluid User Experience of Android
-Mail app is horrible, even Gmail app sucks. All email don't fit into a screen and text is way oversized, even though I set it at smallest setting.
-battery drains during night sleep
-a lot of apps don't match Android UI, thus making the whole user experience very awkward.
-there's NFC chip but there's no way to use it (No Google Wallet)
-Beats Audio is the worst thing I've heard, It doesn't sound any better and in fact it distorts the music by constantly changing bass and treble effect. In my car the music plays through Bluetooth and it constantly clicks like if setting were too high or not balanced. Total joke. It's always turned off on my One X. I'm glad that was an option too.

Overall this is the best Android phone. It will get some time to get used to User Interface since all apps look and navigate different and don't follow Google's design standards. It's probably the best phone HTC ever made. I hope HTC supports future updates of 4.1 and beyond.