Anandtech put the iPad 2 under a GLBenchmark 2.0 test, a great benchmark for seeing the power of the GPU (where Apple is claiming 9x the performance of the original iPad), and came away with some staggering results. The iPad 2, or I guess more specifically, the A5 chip is going to be an absolute beast for 3D gaming. It's incredible, it's almost silly to put the Tegra 2 (which is in the Xoom) and A4 in the same conversation as the A5. Anandtech says:
Developers with existing titles on the iPad could conceivably triple geometry complexity with no impact on performance on the iPad 2. [...] There's just no competition here.
You should check out the rest of the benchmarks at Anandtech. Be sure to see the difference in graphics between the iPad 2 and original iPad with Infinity Blade too. [Anandtech]