Got mine too, so happy!
The back feels so much better than the Galaxy S4.
And the new AMOLED display is amazing. It is seriously much much brighter than the Galaxy S4 or Galaxy Note 3's displays. I tested it out in sunlight and honestly I think it's even better than most LCD displays in direct sunlight.
They seriously focused on improving the display technology this time.
And the camera looks much better than the Galaxy S4, and a solid improvement over the Galaxy Note 3 as well. It can shoot 4K video too, which is amazing for a phone this size IMO.
The new UI seems a lot cleaner than previous TW iterations.
I tested out the heart rate sensor and it's accurate. About the same as I would get if I manually calculated my heart rate. I wouldn't say it's too useful though... unless you're really bored
But as for the phone itself, I'm in love with it.