The Mali-4o0 in Galaxy S II managed to impress this year when it came out in the Galaxy S II. Rumors say that Samsung moved away from PowerVR chips after just one year because they made a deal with ARM to give them early access to the Cortex A7/Cortex A15 big.Little chip design.
So far this deal has paid off, and it will pay off even more when Samsung will be the first one to release a big.Little chip by the end of 2012. That chip will presumably use ARM's new GPU Mali T-604, which should offer several times the performance of Mali-400. While this GPU will be very powerful, it's still a "normal" GPU, meaning it won't take full advantage of the big.Little configuration.
This is why ARM is also preparing Mali T-658, that will build on top of T-604, most likely doubling the performance once again, while also being able to take full advantage of the big.Little configuration. That means not only the CPU's but also the GPU's will become very efficient in the future, and use very little power when performing low-end tasks.
This GPU should arrive by the end of 2013, and both Samsung and LG have already licensed it. If you remember from a while back, LG announced that they licensed Cortex A15 from ARM, and will start making their own chips, just like Samsung, sometime in 2013. So it looks like LG's first chip will be a very competitive one, probably based on a quad core Cortex A15 CPU, with 1-2 Cortex A7 companion cores, and also this new Mali T-658 GPU.
ARM says it will use 8 unified GPU cores and promises the graphics performance of this GPU will be 10x bigger than "current-gen" GPU's (not sure if that means Exynos, or older GPU's). They also say that the GPU will be compatible with the ARMv8 64-bit architecture that's coming out with new CPU's in 2014.
I believe ARM's GPU will begin to get a lot more popular in the mobile market, because of Samsung and LG, two top 5 phone manufacturers, and that's a good thing. The GPU market should be just as "open" as the CPU one, which made ARM so popular because of it's licensing business model. It means the competition will intensify and be stronger than if some proprietary designs won the game. I expect ARM's GPU's to continue to be very competitive with whatever is coming out in the future.