As the second poster mentioned, gaming will be improved significantly. It might not be quite the 60% improvement per Apple's website, and it will vary from game to game, but games that were marginally playable on the 2011 will likely be better on the 2012.
As for the CPU performance, it is definitely better. However, it isn't anywhere near as big a leap as the jump from Core 2 Duo to Sandy Bridge i5/i7 was last year. To put it into perspective, the slowest i5 this year is about as fast as the i7 was last year. Next year's version should offer a bigger CPU boost, as Intel is introducing a new CPU micro architecture. Ivy Bridge is mostly a refinement of the Sandy Bridge chips.