This thread is slowly degenerating...
Overall the GC was between the PS2 and the Xbox.
The PS2 is a pretty powerful (for its time) but unbalanced system with great polycounts, multitexturing, great potential for transparencies and amazing post-processing effects but poor texture filtering often resulting in tons of shimmering.
The Xbox is basically a PC in a box with a so-so CPU, a good fully featured GPU, a good chunk of memory and a HDD. It was the most powerful console of its time and could deliver more modern looking titles plus online gaming and other extras.
The GC has some similarites to the PS2 but taking advantage of that extra year and half to fix some of its problems. It can deliver slightly higher than PS2's polycounts with better lighting, textures and filtering even though it also has some drawbacks like the small amount of fast memory and disc space (problematic for many multiplatform titles) and the limited framebuffer that made many games run in low color depth modes (resulting in dithering or banding, RE4 is a good example, being better overall on GC but running in 32bit color on the PS2).
And since some people are talking about it, the DC pretty much has all the pros and cons of a late nineties PC: nice image quality and texturing but low polycounts with just a base texture and barely any lighting, transparencies or post-processing effects giving it a solid and colorful but sterile look. The small disc space and memory amount would have also been very problematic had the system lasted the whole generation.