Thankfully these headphones have finally come down in price from their original 40 pounds. The initial reviews didn't make any mention of the increase in comfort although the bass is good without going as deep as the DJ-branded sets.
Other differences to the PX200s - they don't fold all the way down like a pair of glasses, the cans just swivel flat (as they are in the packet) so you could use a draw string bag to carry them around.
Best improvements of all, when new anyway, the comfort level is much improved by covering the vast majority of the ear pad, so they shouldn't be wrecked by sweat in a hurry though I still wouldn't leave them on in the rain. Finally, the actual 3.5mm jack plug itself is heavily reinforced. Theoretically you still might be able to fray the single wire there it joins the plug, but it's not nearly guaranteed to happen as with the PX200's plug which was as thin as the main guide wire, all the way down to the jack.
It will add some measure of bass to your existing MP3s, but they won't get any louder so it might be worth re-ripping your favourite tracks to try with the new set.
If your PX200s are broken and in their second year of warranty then these are the next step and you could still RMA the old pair for a backup spare. If you still want the ability to fold all the way down you'll have to check the PX-II range. However for those that prefer to move on, hopefully this price will be the norm for a while and not just for Christmas.