I think a Pokemon can be amazing whether it is detailed or not. Generation 5 didn't exactly have to most detailed designs ever, but they still cut it. For example, the Oshawott evolution line and of course, Scraggy and Scrafty.
However pokemon that are extremely detailed can be memorable, such as Giratina or Palkia, although adding too much detail into one design will more than likely make it look ugly. Perfect example = Barbarcle.
So I think it would be best to make designs somewhere in between?