One thing I would love to see is some enhancements to the level command.
For example, it would be nice if you could use level from a flat tile border rather than having to do it from a flat tile (would make road build a lot easier and making nice slopes easier.
Another thing I would love to see is level raising or lowering the opposite corners to try and keep that border flat. Again it would make road building and slopes much easier. Basically if the 2 corners were higher than the flat tile it would always try and lower the higher of the 2 corners. Conversely, if they are both lower than it would raise the lower of the 2 corners.