Having played around with the One at BB, one thing I really dislike about the One is the button placement (compared to my S3). I can't stand the awkwardly placed/angles power button on the top left, very user UN-friendly IMO. Also I really disliked the flush with the phone volume rocker that's on the right side. The S3/S4 have (IMO) the perfect placements for the volume and power buttons, both of which protrude just enough to make it a breeze to use. I'm sure in time you can get used to the odd layout, but I just didn't find it user friendly. I read a tech site review that also disliked the layout and said on a few occasions they almost dropped their phone trying to fidget with the buttons. Anecdotal of course, but worth noting.
If you are the type to blast your sound w/o using earphone, then this is a cool phone for that. Also, the phone seems sturdy enough, but the back will scratch easily, so most folks will want/need a case to protect it. Battery life has been said to be barely average with mild/medium usage so beware of that as well. Also, this phone uses an older OS I believe as opposed to the S4. Isn't a good chunk of the 32GB of storage eatin' up by software needed on the phone so you won't really get 32GB of storage? I know with my S3 I love being able to pop in an extra 16 or 32GB of storage. Apps/music/video/pics take up a LOT more space than you think, and for me, there's NO WAY I could make it using under 32gb worth of space. That (IMO) would suck to run out of space too soon into the life of the phone.
Other than that, I'm sure it's a pretty solid phone and because it's "new" and the latest flavor of the day, most folks are going ga ga over it, and thus are very passionate about it. In a few days we'll have the S4 readily available and based on how well the S3 did, I'm betting the S4 will be hands down, THE new smartphone to own. Heck BB has opened a giant Samsung S Series kiosk to start selling these new phones (+tablets and accessories). Time will tell if little advertising and little exposure will keep the "One" at the top of folks list of phones to buy.
Should be an interesting year for smartphones for sure. My bet is the iphone (I'm a former 4 year owner) will really start to decline with all these great new Android phone offerings.