It's been mentioned elsewhere, but I am a fan of "Altar of Freedom".
It's got the best command-and-control mechanism of any of these games I've played while retaining what I've always liked about the DBx system.
Between this and Lazyboy's maps, not only will Doug and I finish Shiloh, but I am eager to do a multi-player Antietam, Gettysburg, or Chancellorsville -- all currently-available scenario.
Now if they'd only do a Napoleonic version we'd have something.