Revolution's graphics are still something of a mystery if you think about it; the overall power won't be as high as the PS3, but then again, it won't be rendering in HDTV, just EDTV, giving it a performance boost, so it's kind of a grey area.  In really general terms, the Rev. is double the power of the GC/Xbox, and I'd say Perfect Dark Zero's graphics are not twice as good as Halo 2, so it makes sense that Rev. games will look better than Perfect Dark Zero.  Ok, that was totally overly simplified, but it still makes sense if you think about it. 

Interestingly, Nintendo has suggested that graphics have come to a saturation point, stating that the time when horsepower alone made a difference is over, and that simply beefing up current gen graphics won't allow for most of us to see a difference.  Maybe they're right, and maybe all the extra power in the 360 is unable to make a real difference to the graphical quality we see in Perfect Dark.  Food for thought.  I just can't get over how PDZ is just a tad bit prettier than Halo 2.  I mean, it looked good, and I'll be happy if Rev's graphics are that good, and I'm sure the 360 can do better, but I still keep thinking of what Iwata said: "the time when horsepower alone made a difference is over."