World of Warcraft is probably the best known example of a game whose graphics don't strive for realism, but instead have a cartoony, colorful look. It is sometimes criticized for being unrealistic (or even 'childish'), but this arguably misses the point. A cartoonish style allows boundaries to be stretched, making for stylised, expressive landscapes, buildings and creatures, as well as armor and weapon designs that would otherwise be merely absurd. Fantasy doesn't have to be realistic. WAR also seems to be going down this path.
On the other side, we have games that strive for a realistic look, rather than a cartoonish one: the highly detailed drifts of garbage that litter the City of Villains, the gleaming interstellar behemoths of Eve, and in the fantasy genre, the gushing gore and rippling thews of Age of Conan. Attempting a realistic look can be more immersive, but it can also be harder to engage the player emotionally, not to mention being costly on graphics resources.
Which do you prefer? Do you want your MMOs to look like games, without trying to appear realistic? Or do you disdain the more cartoony styles in favor of realism and detail?