Developer Spellbound Entertainment is bringing the sisters back, with a new game on the DS. The graphical style has changed quite a bit, with smooth backgrounds reminiscent of Cave Story, but the Mario influence is still as clear as ever. Publisher dtp Entertainment is planning a June 2009 release (presumably in Europe, where people know what The Great Giana Sisters is).
It's not new, but if you're so inclined, you can play the original Great Giana Sisters on the DS right now in the form of a homebrew remake.
[Via press release]