While these cards aren't enough of an improvement for 400-series owners to upgrade, their hardware changes are worth noting. They're second-generation Polaris GPUs built on a third-gen FinFET (a type of 3D transistor) architecture. The 400-series cards, meanwhile, were manufactured on a much earlier FinFET process. All of that means AMD was able to make the new cards more efficient, as well as clock them to higher speeds (the RX 580 is around 150MHz faster than the RX 480).
Just like last year, AMD is targeting dedicated gamers who are still running older GPUs, so it's placing a priority on affordability. Prices will fall in line with the previous models, with the RX 580 going for around $229 with 8GB of RAM and $200 with 4GB. The RX 570, which aims for "maximum" 1080p gaming, will go for around $169, while the slightly slower RX 560 will start at $99. At the lowest end there's the RX 550, which AMD sees a step up from integrated graphics for $79. The RX 580 and 570 should hit stores today, while the 550 will come on the 20th. You'll have to wait until May to see the RX 560, unfortunately.
While the 500-series are improvements, they're still very much mid-range video cards. We're still waiting for AMD to announce its high-end Vega GPUs, which will likely go toe-to-toe with NVIDIA's powerful GTX 1080 Ti in the 4K gaming arena. Rumors previously pointed to a Vega announcement in the second quarter, but at this point it seems more likely we'll get something around E3 in June.