According to some documents that have surfaced for No More Heroes 2: Desperate Struggle, the sequel was to have more in-depth revenge missions, along with different character interactions, and multi-faceted missions.
Posted over on AGB, the documents are presented in PDF format, and show not only the stages of the game, but dialogue and the storyline as well.
It's a rather interesting read, as the presentation seems to suggest that the original concept had more depth.
Then again, there is no way to verify the authenticity of the content.
Go have a read anyway.
The Wii-exclusive is out now in North America.