I did a similar thing as the OP and I would like to share my thoughts as well. I come from an iPhone 4 and was blown away by initial impressions of the one X. I was so impressed that I went ahead and bought the intl version for full price, rather than waiting for the att version. But within a week, I put it on craigslist and sold it a couple of days ago ( it took me about 2 weeks to sell the phone

) I am disappointed that I had to sell it off but I could not just stand the numerous issues I had with the phone.
1. Constant crashes and reboots- Many of you would be aware of this. There was a time when I saw the phone sitting on the table just restarted itself 3 times. Shipping with such a buggy software, to me, is just unacceptable!
2.Multitasking - The way multitasking is handled in hox is definitely not right. The applications are not suspended in the background. When you switch and come back, the app is launched again.
3.Bluetooth - Here's the scenario: I have my big music library in the iphone and I keep all the radios(on my iPhone) on all the time. So when I start my car, it automatically connects to the car's Bluetooth and starts playing music. Unless i close my music app going to the app switcher, it always picks the song from where I left off. So smooth and seamless integration.
It just works . When I got my hox, I got the google music uploader and synced my itunes library to gmusic. Now I use my hox to play the music, expect that it doesn't connect automatically. When I tried to connect manually by selecting 'connect' from the car, "portable player could not be connected" ! I had to stop, configure the Bluetooth connection again. This happened about 10 times during my brief stint with the phone.
4.shipped software and update- This may be kinda my fault buying from Negri electronics. The intial batch of white hox shipped in US were mostly from malaysia, not the european version. They were shipped with x.19.xxx version while others had x.28.xx ota. 19, 25,26,28.. why so many different version of what is supposed to be the same version of OS shipped. Not to mention, the phone had a load of crapware from some malaysian carrier. It was unlocked though! The x.19.xxx version was never updated. I would not have cared so much about it if it weren't for the random reboots, crashes and the crappy battery life. My 2 year old iphone 4 has 1.5 times better battery life that this phone. I cannot update the OS myself, cos unlocking bootloader would void warranty. It is htc's job to ship with a less buggy OS; i don't have to rely on xda forums to update this thing myself.
5.smoothness and transitions of the OS I hate to say this, but android still has a long way to go in terms of smoothness and fluidity of the OS. I am not going to go in to specifics here, but it is a bitter truth.
5.Sense yes. In spite of the tone down, sense is still a resource hog. one small example: click on a folder on the home screen; note the lag between your click and the opening of the folder. Now install a third party launcher and see how fast the folder opens. This may be nit-picking but stock android is so much better!
all this being said, the plethora of google apps were great! maps, currents , reader, google + ... Android is feature rich. This is why I have always wanted to own an android device. But the hardware manufacturers keep disappointing me.
some +'s in hox: stunning display, beautiful design(although they screwed up the back camera ,imho ) and awesome camera app/features.
I don't want to get the gNex because of the camera. everything else about gnex is good. I will wait for next galaxy phone before giving android another shot.