If it feels a little too bulky in hand (as compared to say the SGS4 Mini or iPhone 5).
Also if it is confirmed that the Moto X will be on a significantly slower update schedule than Nexus handsets, then ya that might be a deal-breaker.
Re: Why is Samsung so succesful?
Here is an article that I read today which I believe is quite relevant, if you're interested in reading in-depth. And yes - it's about marketing mostly.
How Samsung broke away from the Android pack
Cheers