There's a slide with a block diagram of the Polaris architecture but overall they are a bit light on details. AMD touts performance/Watt as one of the big enhancements and one of the slides claims Polaris will be able to run Star Wars: Battlefront at a Full HD resolution at 60fps while consuming 86W, whereas a card from a competitor demands 140W for the same feat.
Reading the fine print, it seems the test was performed on medium quality settings and the comparison card was NVIDIA's current-gen GeForce GTX 950, which has a lower performance/Watt ratio than NVIDIA's high-end cards. NVIDIA's future Pascal architecture also promises significantly better performance/Watt so the comparison is moot.
The GPU design was modified to include new logical blocks. What’s new is Command Processor, Geometry Processor, Multimedia Cores, Display Engine and upgraded L2 Cache and Memory Controller. Last but not least, the new architecture has 4th Generation Graphics Core Next Compute Units (aka. GCN 4.0).