Everything I knew of Terraria's 1.3 update was shown in that mine cart video. Looking over the vast changelog, there are hundreds of additions, tweaks, and fixes. It's here and it's huge!
Multiplayer is easier to set up, for one. Expert Mode will offer a greater challenge (and better rewards!) for long-time players. There are tons of new craftable items, plus quality-of-life improvements galore. New songs and visuals, too. And Re-Logic is keeping parts of 1.3 a secret.
"What's next? Well, besides any needed hotfixes, we take a deep relaxing breath before we launch headlong into our next projects -- for Terraria, Terraria: Otherworld, and beyond!"
I've got to commend the developers for sticking with the game for this long. Top notch.