Our next release will include some changes that substantially improve performance on Nexus5 without getting updated drivers. Those changes were not ready until just before GDC and therefore not able to make it in to the first release – so look out for them in 4.1!
Our performance on iOS now is right where we expect it to be given the features we support and the full HDR linear lighting pipeline. Android will continue to improve over time as we investigate optimizations to the engine as well as work with IHVs on improved drivers. Again, with 4.1 you should get a better feel for performance on Android going forward.
seenooh makes a good point, though. The mobile temple map and our Soul demo we showed at GDC were both aimed at high end devices: iPhone5S, Nexus 5, Tegra K1, etc. The strategy game demo shows content much more in line with what we expect one would ship a game today.