Mediatek seems on a roll lately. They started out as a low-end chip maker, where they've proved to be a tough competitor for Qualcomm, and lately they've also aggressively begun to compete at the high-end by announcing a true octo-core chip, some more quad-core models with integrated LTE, and now they're also announcing a dual-core (2+2) big.Little chip with Cortex A15 and Cortex A7 cores, that will arrive with the brand new PowerVR Series6 GPU architecture.
While the chip contains 2 CPU clusters, of 2 cores each, Mediatek says it has enabled the "MP" mode, which allows them to use heterogenous computing (at least on the CPU side) with all the cores at once. We'll see what that means exactly, and if it's a more efficient way to use the cores on your device, instead of using the more efficient A7's when you're doing low-end stuff, and the A15's when you're doing higher end tasks.
The GPU inside will be the PowerVR G6200, which should be more powerful than previous Imagination GPU's and other GPU's too. An older benchmark showed it's 3-4x more powerful than a Tegra 3 GPU:
The PowerVR G6200 GPU will also support OpenGL ES 3.0, which is a spec Google has just implemented in Android 4.3 by default, so this chip should work great with Android 4.3 and beyond. Right now, only this one and all the new Qualcomm chips support OpenGL ES 3.0, starting with Adreno 305 (in lower end chips) and finishing with Adreno 320 and the upcoming Adreno 330.
Mali T604 was supposed to support it, too, but for some reason ARM hasn't officially confirmed it yet, but I'm sure the Mali T628 inside the Exynos 5420 will support it.
Tegra 4, unfortunately, is notorious for being the only chip that won't be supporting OpenGL ES 3.0 this year, because it's still using the same old architecture of Tegra 2 and Tegra 3. Nvidia has decided to just wait until Tegra 5 next year, when it will be adding support for the full OpenGL 4.4 spec, making it possibly the most advanced mobile GPU on the market - at least in theory. There are still a lot of things Nvidia could be doing wrong, so it's not an automatic win for them yet. Until then, chip makers like Qualcomm and Mediatek should be coasting in the mobile chip market at least for the next couple of years.