Received them a few days ago, now burning them in.
I was already impressed by the T50p even though as Mike said on Headfonia they were flawed in some aspects. Well the DT 1350 is to me an improvement.
The bass isn't as boomy as with the T50p and there isn't such a huge dip in the upper mids (around 4000 hz). It has kept the T50p strengths (best trebles in a portable headphones, insane details and instrument separation at its price point). I still feel the bass would benefit from a little more damping, but let's see how they'll evolve with additionnal burn in.
As with the T50p I had to bend the headband in to make the sound more substantial and improve bass impact, but it already came with a decent clamping force out of the box (while the T50p was completely unusable the way they arrived).
The T50p already were my favourite portable headphones among the ones I tried (HD-25, ES10, ESW10, ESW9, P5, etc.), but they were definitely flawed. These on the other hand are a marked improvement over the T50p to the point that I'd even say they're a notch above the other portables above.