I like the colour scheme and the Mario/toadstool theme. The forum is fine overall. Here are a few things to consider:
- Your logos are a bit bland. I'm positive you could do better. If you don't wish to change them, use either the red (NF) logo or the black (Nintendo Forums) logo but not both. This will provide you with a less "cluttered" look.
- Consider modifying/converting the red NF image to a favicon.
- Home, Credits, Wii Forums, and Chat seem somewhat detached. Consider combining those menu options with the top menu so you also have less white space and more uniformity in the topmost menu bar.
- Your notice, although necessary, is way too large. This section actually elongates the page and deters from the real hook, your forum content. This also pushes your background image off of most screens upon initial load.
- Consider pulling the background image up a bit so it can be appreciated. It's actually pretty cool.