I haven't used expo on linux, but from what you said, I have the following comments:
1. You can do this - in the all spaces view, drag from one space to another.
2. Agreed, but not a major drawback (see 1). If you use "Warp" You can just hold the window on the edge of a space (in a single space view) for a second or so and it will move to the next space.
http://www.ksuther.com/warp/
3. You can do this - just drag the window (see 1).
4. Customization can be done by adjusting Rows and Columns (+ and -) in the Spaces preferences pane (perhaps expo has more, but the video I have seen only showed 1 row, 4 columns).
5. Set up a keystroke in the pref. pane to show all spaces (if you want all "windows" in ONE space, you can use Expose, but that's not spaces issue).
So check out the options for customization in the preferences - it might make it more usable. No production quality compiz/fusion like "cube" feature exists that I know of (see
http://desktopmanager.berlios.de/ for some related development, or do a search).