This is more a warning than an answer, I'll just post it here because it's too big to fit in a comment.
Be careful with non-standard UIs. For a game, you probably have a bit more leeway.. but check out this article (item 3, specifically) from 1999: http://www.useit.com/alertbox/990530.html
The other warning I'll put out is be careful about putting too much in the context menu.
- It is supposed to be context-sensitive. If you right-click on something, you expect actions for that item you're clicking on, and not a ton of other stuff.
- I hate the fact that Macs don't have right-click by default, but I do actually agree with the supposed original intention (I can't find a reference now, unfortunately): that right-clicking should be a secondary way of accessing items. There should always be another more obvious way of accessing functions (even if it takes longer). Right-click is a shortcut for power users, not the primary mechanism.
It would be helpful to know how many different options you have, and what kind of nesting you can have (eg, is it 20 commands, each 2 or 3 categories deep with 3 or 4 top-level categories? Or is it 400 commands, with 3 top-level categories?).
I'd also suggest, depending on how many, that you try to solve this a different way: don't look for the UI to fit, but consider how you can re-factor your requirements so an extensive UI for hundreds (?) of commands is not needed.