"It is at least a different product, not better or worse."
The very fact that it's different makes it worse for me. I can use Excel 2010 for Windows without thinking about the tool. Small differences like startup behaviour, position of things on the ribbon, and keyboard shortcut force me to think about how to use Excel for Mac, rather than focusing on the task at hand.
Some, but not all, of this is down to differences in the platform and platform-specific design conventions.
