That leak does look pretty cool but I have my doubts that they will get rid of their beloved amoled technology but weirder things have happened. I thought I remember hearing that Samsung was gonna with the curved, nature inspired look for the S4 also.
I think HTC has done a much better job with the "new sense" than the last four versions. Besides the blinkfeed feature, which I'll probably just ignore, the rest of the skin looks much flatter and less 3D than the last version. And it's a phone camera I can care less how good it works long as it can grab those quick shots I am ok.
I don't really see any problem with the two button layout. Least they aren't putting a menu button in. Look at how many iPhones they have sold and they only have one button. Maybe it will take getting used to but again I don't think the two button thing is a deal breaker