Pretty much agree with the post from the_helix.
I think Sony have been clever with this device, they have taken away the things that average/practical users don't really care about.
Do you really need 400+ PPI, 1080p screen, a big internal memory if there's space for a memory card, more RAM etc? They have instead made sure that the processor is top notch, given it 4G and NFC - so you get almost flagship performance at half the price.
Yes some things could be better (there is always something to complain about - the S4 and HTC One are not immune from this either), but with a bigger screen and more robust build than the competition in this price range (the mini S4 and mini HTC One) I think this is the best mid-range phone on the market.
I think it's future proof - but within reason, some games developers always push the boundaries and make software that will only run really well on top devices. I think/hope it will see the next iteration of Android - is it really going to be called kit-kat?